Definition: An interpreted language is a programming language that is compiled into machine readable code at the moment it is run by the languages interpreter. Examples of interpreted languages are Perl, PHP, Ruby, and Python. If you write a program using an interpreted language, you must have the interpreter installed to run that program.
This is in contrast to a compiled language - like C, C++, or Java. These languages are pre-compiled or compiled into machine readable code once by a language compiler. This creates an executable in the machine's native language that can then be run many times.