Transpilation
In plain terms
Converting source code from one language version to another.
Going deeper
Transpilation rewrites code (e.g., modern JS to older JS, or TypeScript to JS) so it runs in target environments. It's a source-to-source compilation step.
Under the hood
Differs from polyfills (which add APIs); Babel, SWC, and the TypeScript compiler are common transpilers.
Examples
TypeScript→JS, ES2023→ES5, Babel, JSX compilation, SCSS→CSS.
Think of it like...
Like translating a modern novel into older English everyone can read.