These are registration rights levels, and they set what can be done with the dogs registration. Pet Only means the dog is registered as a companion, with no breeding rights. Limited Rights allows registration but restricts registering the dogs offspring. Full Rights includes breeding rights. One thing to know up front: a Limited Rights registration can be moved to Full Rights later with the breeders permission, but a Pet Only registration cant be upgraded. Choose the level that matches the dogs role from the start.