MPD is a music server application, this library facilitates communication with it.
MPCLibrary is the library component of the MPC android app. It has no reliance on the app so it is perfectly suitable for a non-android implementation.
This library is not a typical MPD client implementation. MPD playback usually consists of creating playlists and playing them. This library is designed to be used in a more traditional music player fashion where an artist/album/song is selected and played without prior creation of playlists. Please try the app for a better idea of what this means!