FooBar is the association of two metasyntactic variables : Foo and Bar.
FooBar2000 (or just FooBar) is a free audio player (like Winamp) which reads natively many audio formats, like MP3, MPC, OGG Vorbis, etc.
Unlike many audio players such as Winamp or Sonique, it focalizes only on the quality of the sound, and can not be skinned (though colors and title formatting can be modified).
FooBar also has a very flexible plugin system.