Definition of back up
: to accumulate in a congested state traffic backed up for miles
1 : to move into a position behind (a teammate) in order to assist on a play
2 : hold back 1
3 : to make a copy of (a computer file or data) to protect against accidental loss; also : to make copies of all the files on (a hard drive)
First Known Use of back up
Seen and Heard
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