Termed as "the wave" or "wave." When applied in the context of motorcycle riding, "The Wave" is a gesture by you or the other rider that acknowledges another rider's presence. It is usually done when passing the other motorcyclist in the opposite direction, or when you're passing him/her in the same direction or at a stoplight. Common gestures include a quick salute, an outstretched hand or arm or finger. Usually deemed as a "friendly" gesture. Use of derogatory gestures are not considered part of "the wave." Other gestures that can be considered in "the wave" category include nodding of your helmet. "The wave" may not be used by all motorcyclists and some, such as squids, only use "the wave" to acknowledge other squids.
I could tell that guy was a squid... he snubbed my wave