A Veterinary bioscience (also sometimes called bioveterinary science) degree is a 3/4 year BSc degree that covers several aspects of veterinary medicine and animal biology, but will not qualify you to work as a vet. A Veterinary Science degree is a synonym for Veterinary medicine used by some veterinary schools- for example, Bristols veterinary degree goes by this title, and upon completion would qualify you as a vet. I have heard there is some difference between veterinary science and veterinary medicine, but I'm not entirely sure what this difference is other than in name- overall, both would qualify you as a vet.
If you do take a bioveterinary degree and want to train further as a vet, you will need to do either a 4 or 5-year veterinary medicine/science course after you graduate. Other careers within biovet other than becoming a vet do exist as far as I know- research being the main one