Periodic motion likes waves come in many types. Mechanical waves need a medium to travel, electromagnetic waves don’t. Transverse waves vibrate perpendicular to the wave motion, longitudinal waves parallel. Even a simple swinging pendulum exhibits wave behavior. All of these waves can be described in certain ways. They all have speed, frequency, period, amplitude and wavelength. Wave can also combine, or superimpose with each other. This phenomena leads to interference. This can be constructive or destructive interference. In some situations where there is a boundary to reflect from, this leads to a standing wave that seems to sit in one location. This creates points of no movement, nodes, and points of maximum movement, antinodes.