What is the meaning of back up?

verb

• Give moral or psychological support, aid, or courage to.
  • usage: "She supported him during the illness"; "Her children always backed her up"
  • synonyms: support
• Move backwards from a certain position.
  • usage: "The bully had to back down"
  • synonyms: back off, back down
• Establish as valid or genuine.
  • usage: "Can you back up your claims"
  • synonyms: back
• Make a copy of (a computer file) especially for storage in another place as a security copy.
  • usage: "You'd better back up these files"
• Become or cause to become obstructed.
  • usage: "The leaves clog our drains in the Fall"; "The water pipe is backed up"
  • synonyms: clog, choke off, clog up, congest, choke, foul