beating
From Glossary of Meteorology
When two oscillating quantities with different frequencies are superposed, the amplitude of the combination oscillates at the frequency difference, the beat frequency.
The simplest example of beating is the superposition of two equal-amplitude oscillations,
which may be looked upon as an oscillation at the average of the two frequencies with an amplitude oscillating at their difference. Beating is often associated with waves, but nothing restricts it to waves.
