The broad spectrum of abuse is vast. And really hard to put limits on. I'd say that basic things like not providing food, fresh water, shelter, human or animal companionship is abuse. Domesticated animals were domesticated to be our pets, and will resort to wild instincts if left to fend for themselves. Not providing proper health care to an animal, or proper living space for caged animals for example:
Lots of space
Abuse
I think that altering any animal if not used to purpose like to stop breeding, or to fix an internal problem is abuse, using animals for fur, killing wild animals like tigers and elephants for their bi-products is also abuse.