QuakeC was compiled into QuakeVM bytecode, which made all modes and logic portable between platforms without having to recompile things everytime, unlike what had to be done for Quake 2 (which was 100% native code).

This hurt performance a bit but in the longer term benefited the modding scene massively.

It's compiled into bytecode, so it still requires a VM / bytecode interpreter (whatever you want to call it).

Compiled to bytecode.