GLOSSARY: Interpreter

An interpreter is a program that either

executes the source code directly
translates source code into some efficient intermediate code and then immediately executes this
explicitly executes stored precompiled code made by a compiler which is part of the interpreter system

In other words unlike a complier the step of the user intervening by 'executing' or running the program once compiled is missed out.

Interpreting and compiling are the two main means by which programming languages are implemented, they are not fully distinct categories, most of the time some of each form is used in combination.