The returning of a system to a prior known state. A rollback undoes an attempt without pretending it never happened.
Latin rotulare (to roll), from rota (a wheel), joined to Old English baec (back); a rollback turns a system back along the same path it came by, the way a wheel retraces its own turning.
Returning a system to a state it is known to have already held — undoing an attempt honestly rather than pretending it never ran.