Complex sentence: Just in time compilation (JIT) is the generation of executable code on-the-fly or as close as possible to its actual execution, to take advantage of run time metrics or other performance enhancing options.
Split into simpler sentences: Just in time compilation (JIT) is a term now used to describe the generation of executable code on-the-fly or as close as possible to its actual execution. The reason being to take advantage of run time metrics or other performance enhancing options.