backup

noun

• 1help or support:no police backup could be expected
• a person or thing that can be called on if necessary; a reserve:I’ve got a security force as backup the filter is an excellent backup to other systems [as modifier]:a backup generator

• 2 Computing the procedure for making extra copies of data in case the original is lost or damaged:automatic online backup [as modifier]:a backup system
• an extra copy of data from a computer.

• 3North American an overflow caused by a stoppage, as in water or automobile traffic:there are long backups on all routes