Definition: Movement around the vertical axis is the yaw. Typically used to describe unwanted turning or moving in the opposite direction than what was intended.
With some RC airplanes, drag on the ailerons during a banking turn can cause the plane to yaw in the opposite direction -- called adverse yaw.
With RC helicopters, the natural tendency of the helicopter fuselage to rotate in the opposite direction of the main rotor blades is often referred to as yaw. The tail rotor controls compensate for yaw and are used in a rudder-like fashion to turn: yaw left or yaw right.
When boats yaw they are veering off-course or moving somewhat erratically.
