Why would a fuse suddenly trip?

Could you explain why a fuse would suddenly trip? I'm curious about the mechanisms that might cause this to happen. Is it due to an overload of electricity, a short circuit, or perhaps something else entirely? I'm interested in understanding the science behind it and how it protects electrical circuits from damage. Is there a specific threshold that triggers the fuse to trip, or is it more complex than that? I'd appreciate any insights you have on this topic.