The term power cycle, or sometimes called power cycling, refers to the act of turning off the computer and turning it back on immediately. This term could be used to describe this action for any electronic device as well, not only computers.
Power cycling a computer is sometimes done to fix issues with the computer or software program experiencing problems. Power cycling the computer can sometimes help to clear up the errors or issues and get everything to run correctly again. When talking with a computer help desk, their first recommendation is usually to restart the computer, same as power cycling the computer and a good first step in fixing problems.