Compose key

A compose key (sometimes called multi key) is a key on a computer keyboard that indicates that the following (usually 2 or more) keystrokes trigger the insertion of an alternate character, typically a precomposed character or a symbol.

For instance, typing Compose followed by ~ and then n will insert ñ.

Compose keys are most popular on Linux and other systems using the X Window System, but software exists to implement them on Windows and macOS.