back up (Verb) — Give moral or psychological support, aid, or courage to.
back up (Verb) — Move backwards from a certain position. ex. "The bully had to back up"
back up (Verb) — Establish as valid or genuine. ex. "Can you back up your claims?"
back up (Verb) — Make a copy of (a computer file) especially for storage in another place as a security copy. ex. "You'd better back up these files!"
back up (Verb) — Become or cause to become obstructed. ex. "The water pipe is backed up"
back up (Verb) — Move backwards, esp. drive a vehicle backwards.
back up (Noun) — An accumulation caused by clogging or a stoppage. ex. "a traffic backup on the main street" ex. "he discovered a backup in the toilet"
back up (Noun) — Someone who takes the place of another (as when things get dangerous or difficult). ex. "the star had a backup for dangerous scenes"
back up (Noun) — A musical part (vocal or instrumental) that supports or provides background for other musical parts.
back up (Noun) — (computing) a copy of a file or directory on a separate storage device. ex. "he made a backup in case the original was accidentally damaged or erased"
back up (Noun) — The act of providing approval and support. ex. "his vigorous backup of the conservatives got him in trouble with progressives"