OK, this shouldn't be to hard to describe.
A Werecreature is a creature both comprised of human and animal combination either physically, mentally or what have you.
This is like Werewolf but the wolf side (being animal) can be any mamalian animal, I have not seen in written history any non-mamalian Werecreatures.
Were = Man (the creature in question could be female!)
Creature = Another term for a living being that is not humanoid in nature, animal or non-animal, such as an Alien from outerspace could be called a creature as it does not fit the term animal nor human, but animals are also called creatures often as well.