You spell high five, high five.

Because you raise your hand(high) and you have five fingers(five)

A high five A high five

There is most likely a high five each episode. Each one different. Some classic examples have been in Relapse five, Phone five, Cell five, Tiny five, Freeze-Frame high-five, Hypothetical high-five, Wordplay five, Arthritisfive, Self five, Foot five, Claw five, Solemn low-five, Door five, Motility-five, High-six and High two.

because it high in the air and you have 5 fingers.