Definitions of back up:
- verb: make a copy of (a computer file) especially for storage in another place as a security cop
Example: "You'd better back up these files!"
- verb: move backwards from a certain position
- verb: establish as valid or genuine
Example: "Can you back up your claims?"
- verb: give moral or psychological support, aid, or courage to
- verb: become or cause to become obstructed
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