Do book royalties expire?

Excuse me, I'm curious about the concept of book royalties and their expiration dates. Could you please elaborate on whether book royalties ever expire? I've heard varying opinions on this matter, and I'm hoping to gain a clearer understanding. Specifically, are there any legal or contractual provisions that dictate when book royalties might cease to exist? Also, how do these expiration dates, if they exist, differ between various publishing agreements and countries? I'd appreciate any insights you can provide.