A JIT is a just-in-time compiler. As your python code is running, the jit looks for opportunities to take little parts of that python code and compile them into

A JIT is a just-in-time compiler. As your python code is running, the jit looks for opportunities to take little parts of that python code and compile them into executable machine code. Those then run much faster because they don't have to be interpreted instruction by instruction by the python runtime. Not all of the code gets transformed this way so the speedup is modest.