A plant or animal that has come into exsistence from the cross breeding of two species. An example of this is a Muel. The parents are a horse and a donkey, the Muel is not fertile as the parent are not the same species.
A British example of a wild animal is Comic Terns. These are a cross from Common and Arctic. These are rare and rarely survive (though in sea watching Comic Terns are terns which could be Common or Arctic)