back up
phrasal verbback up | back something  up 
- to move backwards, especially in a vehicle
- You can back up another two feet or so.
 - I backed the car up to the door.
 - Can you back your car up so that I can get through?
 
 
back somebody/something  up 
- to support somebody/something; to say that what somebody says, etc. is true
- I'll back you up if they don't believe you.
 - The writer doesn't back up his opinions with examples.
 
 - to provide support for somebody/something
- two doctors backed up by a team of nurses
 - The rebels backed up their demands with threats.
 
 
back something  up  
- (computing) to prepare a second copy of a file, program, etc. that can be used if the main one fails or needs extra support
- It's a good idea to back up your files onto a memory stick.