There can be provisional in person ballots too. You give the voter an envelope to put the ballot in until the provisional status is resolved that hides the votes of the voter.

They're two different concepts, but there's a lot of overlap in the details. Each one must be fully verified before it can be accepted. Provisional usually means their eligibility couldn't be verified at the polling station on election day, for a variety of reasons, but this lets them cast a vote before the deadline while the rest gets sorted out later.