Is Node.js a framework, a library, or a runtime? Explain.

Node.js is a runtime — specifically, a JavaScript runtime environment that lets you execute JavaScript outside the browser.

Why it's a runtime, not a framework or library:

Runtime — provides the environment to run code. Node includes the V8 engine, libuv (event loop and async I/O), and built-in modules like fs, http, and crypto.

Not a framework — it doesn't enforce structure or give you an opinionated way to build apps. Frameworks like Express, NestJS, or Fastify run on top of Node.

Not a library — libraries are code you call from your app (like Lodash). Node is the environment that runs your app in the first place.