There are 2 common meanings:

1/Used in military or police force: Reinforcements, support, help.

2/Computer using: create your secured data in case the computer goes down suddenly, mainly to prevent data loss.
1/Police officer shouts via radio: "Shot fired, shot fired. Officer down. Unit 26 to base, we got a situation here. We need back up immediately!" - "Roger, just hold on. Back up are on the way."

2/Before installing Smart Windows Care, we strongly recommend you to back up you data first to prevent yourself from losing important data.
by Mr. Bum Bum November 13, 2010
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More comfortable way to say tampons or maxi pads in public.
"Hey, can you check aisle 2 for tampons back up for me?"
by Elliegold April 16, 2014
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When you drive your car in reverse, you back up.
That moron scratched his car when he backed it up.
You should use both side and rear mirrors when you back up your car.
by BMatty November 26, 2010
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A dancefloor technique to attract the attention of a partner. Essentially this involes backing your bootie towards your partner and getting close, often thrusting. This technique will initiate a grind type of dancing.
She's backing-up to you dog! Get in

Let's get on the dancefloor dog. We can back-up on those hotties over there
by Dykester January 15, 2007
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An unusually large amount of semen stored in a man's body due to lack of ejaculation
I haven't jacked off in weeks. I'm backed up.
by Mudesi December 23, 2004
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To carry on drinking alcohol after vomiting due to excessive boozing
Barry did a great job of backing up after his last vomit
by Rahoolduke August 20, 2007
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