The audience performs a wave by standing up in successive order. As soon as one person stands, the person standing next to them begins to stand and the first person sits down. From a distance this appears as a wave moving through the audience.
How it Happens
Audience Wave demostrates the way that traveling waves work, where the high point of the wave moves across the crowd as the people in the crowd stand up.
Traveling wave: a wave form where the high and low points of the wave move through the medium.
Medium: the thing the wave is moving through, be it air, water, or in this case, the audience.