back up
back up , intransitive verb
1.
to move in a reverse direction; -- used of vehicles or animals.
2.
to accumulate due to a blockage of flow; as, a traffic backup due to an accident; a sewage backup.
back up , transitive verb
1.
to serve as a backup{3} for (another person or persons); as, the patrolmen backed up the detectives as they went inside to make the arrest; the center fielder backed up the shortstop on the play.
2.
(Computers) to make a backup{5} of; as, the sysop backed up the purchasing data files every night.