Definition: interpreter

A high-level programming language translator that translates and runs the program at the same time. It converts one program statement into machine language, executes it, and then proceeds to the next statement. This differs from regular executable programs that are presented to the computer as binary-coded instructions. Interpreted programs remain in the source language the programmer wrote in, which is human readable text.

Multiplatform Runtime Modules
A major advantage of an interpreted language is that it is generally able to run on more than one hardware platform. The source code is the same, but the actual interpreter software ("runtime module") converts the source into machine language. The interpreter must itself be in the native machine language of the hardware it runs in, which means changes in the language require updated interpreters for each hardware platform.

Slower, But Easier to Test
Interpreted programs run slower than their compiler counterparts. Whereas the compiler translates the entire program before it is run, interpreters translate a line at a time while the program is being run. However, it is very convenient to write an interpreted program, since a single line of code can be tested interactively.

Some languages can be both interpreted and compiled, in which case a program may be developed with the interpreter for ease of testing and debugging and later compiled for production use. See JIT compilation.

Intermediate Languages - Compiled and Interpreted
Languages such as Java and Visual Basic are compiled into an intermediate bytecode language that still requires a runtime module (see illustration below). See Java and Java virtual machine.

Interpreters vs. Compilers

Unlike compiled languages that are translated entirely into machine language ahead of time (right), interpreted languages are translated at runtime. Java and Visual Basic interpreters (center) translate "bytecode," which is an intermediate language compiled from the original source code.