A hybrid is the offspring of two different species of animal, which shares elements of both of its parents' species. The "hybrid" tag should be applied to images and animations containing characters who fit that bill.
A slightly-less well known fact about hybrids is that the exact animal that results is different depending on which parent was which species. The most common hybrid in the real world, for example, is the mule, which is the offspring of a female horse and a male donkey, with the opposite gender combination leading to an offspring called a hinny.
Hybrids in the real world are not very common; most species are incapable of reproducing with each other, and most hybrids are born sterile, meaning that they cannot naturally reproduce (the only way to get more mules is to mate more male donkeys to female horses). Of course, Furry covering the realm of fiction, such rules can easily be ignored.