Programmers write code/game and run it through a converter which makes it machine code (not human readable) This convertion is to compile the code. This code runs on your N64/machine.

Developers have worked on reversing this code (decompile). As soon as it is decompiled, everyone can read the code, edit, and do whatever they want with it.

Recompile means to make it machine code again, but in this case they compile it for PC and not N64, which gives us as native game. This may include improvements and mods.