A compiler that converts all of the bytecode into native machine code just as a Java program is run. This results in run-time speed improvements over code that is interpreted by a Java virtual machine.
A compiler that takes Java byte code and converts it to more efficient machine-specific code. This is done at run-time.
A program that turns Java Byte code into processor-specific executable software. Just-in-time (JIT) compilers can help overcome the sluggish performance of a Web browser's virtual machine, which runs byte code one instruction at a time