What is meant by 'bleeding' a plumbing system?

"Bleeding a system" consists of opening the topmost valve and letting all the air escape out of the lines under pressure. That's for house water piping.
To bleed a pump system you shut the pump off and open up the uppermost cold water faucet, (to prevent air lock) and opening up a faucet or boiler drain near the pump and draining the system. Why do you ask? If you have no hot water pressure to your bathroom tell me about it. Bleeding the system won't help. 'What faucets are affected? The brand? How old? One handle or two knobs? Give me something towork with here? Cheers, Tom

1 handle kitchen sink faucet has no hot water pressure. Had a new hot water tank install.