Mudras are hand and body positions that carry meaning. The word comes from Indian
culture (Southeast Asia, not North America).
Mudras are used in dance, art and simple sign language and are most often expressions of emotion used to accent communication. In American culture, I have heard the middle finger extended in a "fuck you" situation described as "the one-finger mudra of contempt." In actuality, this is a fairly accurate example of how mudras accent conversation. In my opinion, they may be equated with the modern written symbology of emoticons.
For a science fiction book depicting mudras in action and how they affect a culture, check out Walter Jon Williams' text Aristoi.