Animation of harmonics: illustrating how an oscillator (such as a guitar string) can vibrate at different frequencies. The lowest frequency (in red at the bottom) is called the fundamental frequency. Increasingly higher harmonics are seen receding into the distance. The undulating strips are fixed at either end to boxes and so these points are nodes. Non-moving parts of the strips are also called nodes. The parts that move maximally are called antinodes. These oscillations are called standing waves because they do not progress anywhere. They are created inside an oscillator as the waves bounce back and forth, interfering with each other. This is how musical instruments produce pleasantly sounding harmonics.