What is the meaning of Hi5?

An air five is a variation where the hands of the participants never actually touch, needing only line of sight to make the gesture. It has an advantage for participants who are otherwise too far apart to achieve physical contact at the moment of the gesture.

Is high five a word?

or high five Informal. a gesture of congratulation, solidarity, or greeting in which one person slaps the upraised palm of the hand against that of another.