What is the meaning of the idiom "Bone of contention"?

The idiom "bone of contention" means a subject of dispute. It is often used to describe something that two or more people cannot agree on, and that is a source of conflict between them. The idiom comes from the idea of two dogs fighting over a bone.

The other options are incorrect. "A common goal" does not mean a subject of dispute. "A subject of peace" does not mean a subject of dispute. "Love for dogs" is not a subject of dispute.