The name was said to have signified 'the country of Balar', and to have been given at first to the lands about the mouts of Sirion that faced the Isle of Balar. Later the name spread to include the all the ancient coast of the northwest of Middle-Earth south of Firth of Drengist, and all the inner lands south of Hithlum and easwards to the feet of the Blue Mountains, divided by the river Sirion into East and West Beleriand.
Beleriand was broken in the turmoils at the end of the First Age, and invaded by the sea, so that only Ossiriand (Lindon) remaind.
Information for this node was taken from the index of the Silmarillion by Tolkien