Actually there isn't. Every project, no matter how it's managed, changes as it goes on. It has to because you learn and discover things along the way. That's why maintaining and understanding project requirements and how they've changed is incredibly important. If you don't keep on top of them then you end up with a project that wanders all over the place and never finishes. Or you build something that misses out important features. Or the project costs far too much. Requirements are not tasks, or epics, or things you're working right not. They're the goals that the tasks and epics work towards.

(My first startup was a requirements management app.)