Powertyping is when you pretend to type in a orderly manner REALLY fast, but actually typing random nonsense. Basically a more sophisticated way of saying you're spamming, and to confuse people.
Bob: I'm powertyping on Tom's chat!
Rick: What.. the hell..
/Tom joins the conversation.
Tom: STOP, YOU FUCKHEAD.
Bob: ghih4weigqegiqhieqhogehog qehogjehgkhbcjkgnsjkgnwjkesgthiesbdgjkeqnjkdthgiuwehtgkw4hesjgkvensdjkgehwdTgwhjesdgbjkvrsdngjkwrsfyjhwrjkghrbfgry
erkhrefherjkdfghklfngklrwjhowrjfhklwrhkjbrkljhklrejfklhjtkljfh
Rick: ...oh.