What is a spazz i have no clue?

The word spazz is a slang derivative of the word spastic. Most commonly people crudely referred to a person with cerebral palsy where a person's legs and arms and other muscle groups twitch and jerk around uncontrollably. Spastic movement is the word that describes a person so afflicted. It was shorted to spazz as a slang word to mean pretty much what everyone else here has described.