to support (somebody) in an argument or proposal
to give support to (an argument, etc)
in computing, to make a security copy of (data, a file, etc)
to hold (something) back; to cause (something) to accumulate
The dam was backing up an immense quantity of water
in computing, to make a copy of data, a file, etc, esp for security reasons
said of traffic: to form an increasing queue behind a hazard or congestion
in cricket, said of the non-receiving batsman: to move forward down the wicket when the ball is bowled to be ready to make a run