Interpreter

An interpreter is a piece of software that parses a high level language so that it can execute actions on a computer. The best interpreted language will always be slower than a compiled language like C++, because the compiled code is run directly. Examples of Interpreted languages:
 * GML
 * Flash ActionScript 1.0/2.0/3.0
 * JavaScript
 * Java

Just In Time
"Just In Time" compilers are interpreters which precompile (either partially or fully) their source files as and when they need to. Python is an example of a Just-In-Time compiler. One advantage these languages have is that the precompiled source files can be distributed.