A scope change is any change request by any of the stakeholders. The change request can be approved or unapproved, if it's approved then it's a controlled change. Significant scope changes (that are approved) can cause the project manager to re-baseline. The CCB (change control board) is usually responsible of approving large scope changes (small changes can be directly approved by the project sponsor).
If the change request is unapproved, and yet it is being processed by the project manager (maybe to hide the fact that he didn't collect the requirements properly), then you will have scope creep (which may delay the project, increase the costs, and ironically, reduce the scope). In other words, scope creep stems from an uncontrolled scope change.
Rigid scope control, constant and honest communication with all the stakeholders, and immediate re-baselining after large change requests ensure that scope changes will never morph into scope creeps.