How long do book royalties last?

I'm curious, could you elaborate on the duration of book royalties? Are they perpetual, or do they have a specific lifespan? I've heard varying opinions on this matter, and I'm interested in gaining a clearer understanding. Is there a standard contract term that outlines how long an author can expect to receive royalties for their work? Additionally, do factors such as the book's popularity or genre impact the duration of royalty payments? Your insights would be greatly appreciated.