From Rosetta Code
GHC is an implementation of Haskell. Other implementations of Haskell.
The Glasgow Haskell Compiler (or GHC) is a compiler for the functional programming language Haskell. GHC includes an interactive environment for Haskell, known as GHCi.

It is also the de-facto testbed for new features, with useful ones eventually being adopted into the language standard.