Framework
The Quick Version
A pre-built structure so you don't reinvent everything.
How it actually works
A framework provides routing, rendering, build tooling and conventions so you write features instead of plumbing. React, Vue and Svelte handle the UI; Next.js, TanStack Start and Remix add full-stack structure around them.
Why does it matter?
Your hosting platform asks which framework you used so it knows how to build your project.
Example
React + Vite is a very common beginner stack.