JIT compilation means compiling code on the fly right when you're about to execute it. When the code is part of a larger program, jitting allows to compile the parts of it you actually need and avoid wasting time to compile other parts. It also allows to compile the relevant code paths based on dynamic flow analysis, which often involves interpreting your program the first time you run it and emitting instructions for the next time around (tracing)

If the code unit is small and you know you're going to run it all, you can compile it in one swoop. If you compile it when you load it in the kernel, as opposed to compiling it lazily right before you run it the first time, i think it's fair to call this Ahead-of-Time compilation, even if the compilation happens right next the use site and not as part of the developer tool chain