The Animal Kingdom

I am sick of how animals are classified.  It is too confusing with all the Greek names.  I have a simple way of classifying things.  Anything that flies will be a bird.  Anything on land will be animal.  Anything that swims is a fish.  It will also be dependent on where that creature is at said time.  If a bird is walking on land it will then be an animal.  An otter on land would be an animal, but a fish when it is in water.  Simple.