Glossary
Scope
A scope names one specific capability an application is requesting — read a calendar, not modify it; see a profile name, not an email address — rather than a blanket grant of everything the underlying account can do. The user approving the request sees, or should see, exactly what's being asked for, narrowed to that one capability.
Scopes are only as protective as how carefully an application requests them. An application that asks for far more scope than its actual function needs, on the theory that it might be useful later, erodes the entire point of scoping — the user is back to granting broad access, just with an extra approval screen in the way.