A farting sound produced by clasping both hands together so that air is trapped between the palms, then squeezing so that the air must escape by vibrating the skin of the palms. This can also be produced by pulling air back into one's hands after the air has been squeezed out. Some people are so 'talented' at this that they can play rather complex music with it. One who is skilled at producing hand farts is called a 'manualist'.
Whoa! That guy just played the Star Wars imperial march with hand farts!