Noun backup has 5 senses
  1. backup - an accumulation caused by clogging or a stoppage; "a traffic backup on the main street"; "he discovered a backup in the toilet"
    --1 is a kind of
    accretion, accumulation
    Derived form: verb back up5
  2. stand-in, substitute, relief, reliever, backup, backup man, fill-in - someone who takes the place of another (as when things get dangerous or difficult); "the star had a stand-in for dangerous scenes"; "we need extra employees for summer fill-ins"
    --2 is a kind of peer, equal, match, compeer
    --2 has particulars:
     locum tenens, locum; double, stunt man, stunt woman; surrogate, alternate, replacement
  3. accompaniment, musical accompaniment, backup, support - a subordinate musical part; provides background for more important parts
    --3 is a kind of part, voice
    --3 has particulars: descant, discant; vamp
  4. backup, computer backup - (computer science) a copy of a file or directory on a separate storage device; "he made a backup in case the original was accidentally damaged or erased"
    --4 is a kind of duplicate, duplication
    Derived form: verb back up4
  5. backing, backup, championship, patronage - the act of providing approval and support; "his vigorous backing of the conservatives got him in trouble with progressives"
    --5 is a kind of blessing, approval, approving
    Derived form: verb back up1