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Interpreters take the source code and interpret it one line at a time and execute that line then go onto the next line

Compilers convert the entire program into the machine language of the hardware all at the same time.  The file containing the machine code can then be executed.

JIT compilation (Just In Time Compilation) take the source or bytecode (in Java's case) and converts all or part of it into the machine language of the hardware, stores the code in memory and then executes it.  In JIT some of the code can be compiled and some interpreted depending on the JVM being used.