Men, living in the vales of the river Anduin. They were descendants of the Edain or their close kin, related to the Northmen of Rhovanion (and therefore the Rohirrim) and the Bardings of Dale. After the WotR they were given the major part of ErynLasgalen.
At the time of the WotR Beorn was their leader, though - as a skinchanger - he was probably not representative for the Beornings in general. The Beornings aided Aragorn in his search for Gollum late in the Third Age.
Beornings were famed for their honey-cakes.