Scope is what is included. Scope creep is the accumulation of small additions nobody priced, each of them reasonable on its own.
Nobody agrees to do fifty per cent more work for nothing. They agree to one quick thing, eleven times. Each is too small to invoice and too awkward to refuse, and together they are the margin.
Refusing feels petty and risks the relationship, particularly when the client is pleasant and the request is genuinely small. So the moment to address it is never this request — it is the agreement, before any of them happen.
The fix is not saying no. It is saying 'yes, and here is what that changes' — which is a different conversation and a far easier one.
What is included, what is explicitly excluded, how many rounds or revisions, what happens when something extra is asked for, and what it costs. The exclusions do more work than the inclusions.