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
Get the Back up mug.
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
Get the back up mug.
When cheapass loser fucking hillbilly thinks he is getting screwed out of overtime.
They are not giving me any jobs, the are backing them up for John.
by doughboy2 May 12, 2009
Get the Backing them up for John mug.
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
Get the back-up mug.
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
Get the backed up mug.
To back it up and get down.

An ancient saying, originating in Mesopotamia, recently reintroduced by rapper Pitbull in the song 'On the Floor' by the Jennifer Lopez.
Moments after entering the club, Matthew backed it up like a Tonka truck.

Joseph ordered a root beer at the bar, then proceeded to back it up like a Tonka truck.
by grandmaster_phag June 29, 2016
Get the back it up like a Tonka truck mug.