back•up (bak´) adj.
1 standing by as an alternate or auxiliary [a backup pilot]
2 supporting [a backup effort]
3 of or having to do with the backing up of computer data, files, etc.
–n.
1 the act or result of backing up
a) an accumulation because of a stoppage
b) a support or help; specif., a person or thing available for service on an emergency basis or as a substitute
c) in jazz and popular music, musical accompaniment, as that provided by a singer or instrumentalist; also, such a singer or instrumentalist
2 Bowling a ball that follows a path opposite to that of a hook: in full backup ball 3 Compute
a) the act or an instance of backing up computer data, files, etc.
b) a backup copy of data, a file, etc. see the phrase back up (sense 5) under BACK1