Just-In-Time compilation (JIT) is a technique used to improve the performance of interpreted code by translating it to machine code.
Introduction
From Wikipedia:
In computing, just-in-time compilation (JIT), also known as dynamic translation, is a method to improve the runtime performance of computer programs based on bytecode.
JIT compilers represent a hybrid approach, with translation occurring continuously, as with interpreters, but with caching of translated code to minimize performance degradation. They also offer handling of late-bound data types and the ability to enforce security guarantees.
In a bytecode-compiled system, source code is translated to an intermediate representation known as bytecode. The JIT compiler reads the bytecode and compiles it dynamically into machine language so the program can run faster.
Tag usage
Use the jit tag for questions about JIT compilers. Be sure to include other relevant tags as well. For example, if your JIT question is Java-specific, include the java tag.