Babel is a JavaScript compiler, or transpiler, that converts code written with modern syntax into equivalent JavaScript that older browsers, Node.js versions and embedded runtimes can execute. It parses source into an abstract syntax tree, applies a chain of plugins and generators, and outputs readable code together with optional source maps.
The site provides a getting-started guide, documentation for presets such as env, TypeScript and React, the plugin authoring handbook, configuration file formats, the REPL where transformations can be tried interactively, and explanations of how core-js and polyfills relate to syntax transforms and target browser lists.
It suits teams shipping applications to a broad browser matrix, library authors who must publish compatible packages, projects gradually migrating from JavaScript to TypeScript, and build-tool maintainers who need a configurable transformation layer inside a larger bundling pipeline.
Compared with a native modern runtime it adds a build step and configuration overhead but decouples the language features you write from the environments you support; compared with a simple minifier it works on syntax rather than whitespace, though many newer bundlers now include their own transform step.
Keep preset-env targets aligned with the browserslist file, avoid shipping unused polyfills to every bundle, pin plugin versions because transform ordering matters, and check the REPL before debugging an unexpected output since most surprises come from configuration rather than the compiler itself.