definition of
back up

[1] #1 back up v. give moral or psychological support, aid, or courage to; "She supported him during the illness"; "Her children always backed her up". wn

[2] #2 back up v. move backwards from a certain position; "The bully had to back down". wn

[3] #3 back up v. establish as valid or genuine; "Can you back up your claims?". wn

[4] #4 back up v. make a copy of (a computer file) especially for storage in another place as a security copy; "You'd better back up these files!". wn

[5] #5 back up v. become or cause to become obstructed; "The leaves clog our drains in the Fall"; "The water pipe is backed up". wn