Is oxtail really ox or cow?

I'm curious, could you please clarify something for me? The term 'oxtail' is often used in culinary contexts, but it's not entirely clear to me if it refers specifically to the tail of an ox or if it's interchangeable with the tail of a cow. Is there a distinction between the two, or is 'oxtail' simply a generic term used to describe the tail of any bovine animal? I'd appreciate any insight you can offer on this matter.