Tech terms explained: IaaS vs PaaS vs SaaS, AWS and more.

A website or app proposal can read like a foreign language. One supplier suggests AWS, another builds on Firebase, a third offers a headless CMS written in TypeScript. Every one of those words hides a decision about cost, control and who maintains what, and you are the one asked to sign.

This glossary gives you each term in one or two plain sentences, then what it means for your business. We design websites in Figma, build them in Astro and host them for our clients, so these words come up in our work every week. Every fact below was checked against official documentation in October 2026, with links so you can read the sources yourself.

IaaS vs PaaS vs SaaS: cloud computing explained

Cloud computing means renting computing power, storage and software over the internet instead of buying and running your own hardware. IaaS, PaaS and SaaS are its three service models. They differ in how much of the technology the provider runs for you, and how much you run yourself.

The definitions most of the industry still uses come from the American standards institute NIST, which published The NIST Definition of Cloud Computing in September 2011. NIST describes cloud computing as on-demand network access to a shared pool of computing resources that can be provisioned and released with minimal management effort. It names exactly three service models:

• IaaS (Infrastructure as a Service) gives you the raw building blocks: virtual servers, storage and networking. You install and maintain the operating system, the software and the data.
• PaaS (Platform as a Service) gives you a ready environment for your own code. The provider maintains the servers, the operating system and the runtime. You bring the application.
• SaaS (Software as a Service) gives you finished software in a browser or an app. The provider runs everything. You manage your users, your settings and your data.

An office makes the difference tangible. IaaS is an empty office floor: you furnish it, wire it and keep it clean. PaaS is a serviced office: the desks and the internet are there, and you bring your work. SaaS is a meeting room booked by the hour: you walk in and use it.

Which model is your website on?

Your website already runs on one of these models, whether anyone told you or not. A Squarespace, Wix or Webflow site is SaaS: you rent the builder and the hosting as one product, and the platform handles the updates. A WordPress site on a virtual server is IaaS: flexible, but every update and security patch is your job or your supplier’s. A site built with a modern framework and deployed to a hosting platform such as Netlify or Cloudflare sits closest to PaaS: the platform runs the servers and the network, and your developers own the code.

None of these is wrong. What matters is who carries the maintenance, and whether that is written down. When you compare proposals, ask two questions: which model does the site run on, and who patches it?

What is AWS?

AWS (Amazon Web Services) is Amazon’s cloud computing platform. It rents out servers, storage, databases and over 200 other services over the internet, with pay-as-you-go pricing, to companies of every size.

AWS started inside Amazon. The company says it launched Amazon Web Services in the spring of 2006, after experiencing first-hand how hard and expensive it was to run IT infrastructure for Amazon.com. The storage service Amazon S3 came first in 2006, and the computing service Amazon EC2 followed a few months later. Today AWS is Amazon’s cloud computing division, led by CEO Matt Garman. Customers sign their contract with an Amazon subsidiary: Amazon Web Services, Inc. in Seattle, or Amazon Web Services EMEA SARL in Luxembourg for most customers in Europe, the Middle East and Africa.

How does AWS work?

You create an account, choose services in a web console or through code, and pay for what you use, such as hours of computing or gigabytes stored. AWS is mostly IaaS and PaaS: it sells building blocks, not a finished website. The services you will hear about most:

• Amazon EC2: virtual servers.
• Amazon S3: storage for files and backups.
• Amazon RDS: managed databases.
• AWS Lambda: runs code without you managing a server.
• Amazon CloudFront: a content delivery network that serves files from locations close to your visitors.

What AWS means for your business

Most company websites do not need their own AWS account. AWS makes sense when you run custom software, store large amounts of data or need one specific service, and when you have people who can configure it, secure it and watch the bill. It is a toolbox, and someone has to choose the tools.

For European companies with strict data requirements, one development is worth knowing: in January 2026 Amazon made its AWS European Sovereign Cloud generally available, a separate cloud located entirely within the EU, with its first region in Brandenburg, Germany.

What is Firebase?

Firebase is Google’s platform for building and running web and mobile apps. It bundles a database, user sign-in, file storage, hosting and server code into one service, so a small team can launch an app without managing servers.

Firebase started as an independent startup and joined Google in October 2014. In that announcement, co-founder James Tamplin wrote that 110,000 developers were using it. Today Firebase runs on Google Cloud infrastructure. What it offers:

• Cloud Firestore and Realtime Database: cloud databases that keep data in sync across devices in real time.
• Firebase Authentication: sign-in for your users, by email, phone or an existing account such as Google.
• Cloud Functions: backend code that runs in response to events, without servers of your own.
• Hosting and App Hosting: web hosting with your own domain and SSL.
• Crashlytics, Analytics and Cloud Messaging: crash reports, usage data and push notifications.
• Firebase AI Logic: a way to call Google’s generative AI models directly from an app.

You start on the no-cost Spark plan, with usage limits, and move to the pay-as-you-go Blaze plan as you grow. Developers often call Firebase a backend as a service: it sits between PaaS and SaaS. Your developers write the app, and Google runs the pieces behind it.

What Firebase means for your business

Firebase fits a first version of an app, a customer portal or a mobile app with logins and notifications, built quickly by a small team. Weigh three trade-offs before you commit. Your data and code become closely tied to Google’s services, so moving away later costs time. Usage-based pricing grows with your success, so ask for a cost estimate at ten times your expected users. And Google retires individual products: Firebase Dynamic Links shut down on 25 August 2025. For a marketing website, Firebase is usually more than you need.

What is TypeScript?

TypeScript is a programming language from Microsoft that adds types to JavaScript. It is a superset of JavaScript: it keeps JavaScript’s syntax, adds labels that describe what kind of data each piece of code expects, and compiles back to plain JavaScript that runs in any browser.

Microsoft unveiled TypeScript publicly on 1 October 2012, as a free and open-source project. The official site, typescriptlang.org, sums it up as “JavaScript with syntax for types”. TypeScript code converts to JavaScript, which runs in a browser and on server runtimes such as Node.js, Deno and Bun. In 2026 the team released TypeScript 7.0, a native port written in Go that Microsoft describes as 10x faster.

What TypeScript means for your business

Types catch mistakes before code goes live. They also make a codebase easier to hand over to another developer, and easier for editors and AI coding assistants to understand. When you buy a website or app, ask whether it is written in TypeScript. It is a sign of maintainability, not a guarantee. Astro, the framework we build with, uses TypeScript to validate content: a page that misses a required field fails the build instead of going live broken.

What is a headless CMS?

A headless CMS is a content management system without a built-in website. Editors write and organise content in it, and the CMS delivers that content through an API to any website, app or screen. The “head” is the presentation layer, and a headless CMS leaves it to a separate front end.

A traditional CMS such as WordPress stores your content and also renders the pages. A headless CMS splits those jobs: the content lives in the CMS, and the website is built in a framework such as Astro that fetches it.

Strapi

Strapi is an open-source headless CMS. Developers define the content structure, editors work in an admin panel with role-based access, and the content is available through REST and GraphQL APIs. You host Strapi yourself or on Strapi Cloud, the company’s fully managed hosting. The name comes from the project’s original purpose: to help you bootstrap your API.

Sanity

Sanity is a hosted content platform. Editors work in Sanity Studio, a customisable editing app where several people can work at once. The content lives in the Content Lake, Sanity’s real-time database for structured content, and developers query it with GROQ, Sanity’s own query language.

What a headless CMS means for your business

A headless CMS earns its place when many editors publish often, or when the same content feeds a website, an app and a newsletter. For many company websites, content in plain Markdown files is simpler and leaves nothing extra to pay for or maintain. We explain where that line sits in our guide on when Sanity beats Markdown.

COTS software vs custom software

COTS stands for commercial off-the-shelf: ready-made software that anyone can buy, rent or license. Custom software is built for one organisation and its specific way of working.

NIST defines COTS as “a software and/or hardware product that is commercially ready-made and available for sale, lease, or license to the general public” (NIST glossary). The term is sometimes misheard as “common off the shelf”, but the C stands for commercial. Most SaaS tools are COTS delivered from the cloud: Microsoft 365, Shopify and HubSpot are all examples.

Buy, build or connect

A useful rule: buy COTS for everything that is standard in your industry, such as bookkeeping, email and CRM. Consider custom software only where it is what sets you apart. Often the gap between two off-the-shelf tools is better closed with an automation, for example in n8n, than with new software. If a custom build is on the table, our guide on having software built covers how to approach it.

What is Astro?

Astro is an open-source web framework for content-driven websites, such as marketing sites, blogs and online shops. It renders pages on the server and sends zero JavaScript to the browser by default, so pages load fast and search engines read them easily.

Astro calls its approach islands architecture: the page is plain HTML, and only the parts that need interaction, such as a booking widget, load JavaScript. It works with components from React, Vue, Svelte and other libraries, and its content collections validate every page against a schema. In January 2026 Cloudflare announced it was acquiring The Astro Technology Company, the team behind Astro. Astro stays open source, and you can host it on Cloudflare or anywhere else.

Astro is the framework we build client websites with. We design in Figma, build in Astro and keep your content in plain files that you own. If you want to see how that works, start with our Astro guides or follow the steps to make an Astro site yourself. For brands whose marketing team wants a visual editor, we explain when a Webflow agency is the better choice. Our webdesign service shows how a project runs from strategy to launch.

How we help

You do not need to master these terms to make a good decision. You need a partner who explains the trade-offs in your language and then takes care of them. Viralistic is that partner for established businesses and premium brands: one strategic lead instead of a stack of freelancers.

We design your website in Figma and build it in Astro through our webdesign service. Projects start around EUR 4,000, and larger CMS-driven platforms can reach EUR 20,000 or more. After launch, managed hosting keeps the site live, fast and secure, with one person to call for domain, DNS, SSL, email and updates. If you are still comparing options, read what goes into having a website built before you request quotes.

Frequently asked questions

What does AWS stand for?

AWS stands for Amazon Web Services. It is Amazon’s cloud computing division, launched in 2006, and it rents out servers, storage, databases and more than 200 other services over the internet. Businesses pay for what they use instead of buying their own hardware. Customers in most of Europe contract with Amazon Web Services EMEA SARL, a subsidiary based in Luxembourg.

Is Firebase owned by Google?

Yes. Firebase began as an independent startup and joined Google in October 2014. It is now Google’s platform for building web and mobile apps, and it runs on Google Cloud infrastructure. Your app’s database, sign-in, hosting and server code can all run on Firebase, which also means your app depends on Google’s pricing and product decisions.

Is ChatGPT SaaS or PaaS?

ChatGPT, the app you log in to and use, is SaaS: finished software that the provider runs entirely. The OpenAI API that developers build their own products on behaves more like a platform service, because your team writes the application and the provider runs the models underneath. The same company can sell both models.

Do I need AWS for my business website?

Usually not. A company website runs perfectly well on a website builder or a managed hosting platform, without its own AWS account. AWS makes sense for custom software, large data volumes or specific cloud services, and only when someone can configure, secure and monitor it. Ask your supplier who manages the account and who receives the bill.

What does COTS stand for?

COTS stands for commercial off-the-shelf. It describes ready-made software or hardware that anyone can buy, lease or license, such as Microsoft 365 or Shopify. The opposite is custom software, built for one organisation. Most businesses run largely on COTS and build custom software only where it gives them a real advantage.

Is TypeScript the same as JavaScript?

No. TypeScript is a superset of JavaScript made by Microsoft: it adds types on top of JavaScript and then compiles back to plain JavaScript. Browsers run the JavaScript, not the TypeScript. Developers use it because type checks catch mistakes before code goes live and make large codebases easier to maintain and hand over.