Tremolo
The effect that rhythmically raises and lowers volume, driven by a slow oscillator.
An LFO running at a few hertz swings the gain up and down; depth sets how far the level dips, rate how often. A sine wave gives a gentle pulse, a square wave a choppy on-off that sounds like someone flicking the volume knob very fast. Guitar amplifiers had it as early as the 1940s and 50s, back then as a tube whose bias was swept by an oscillator.
The names got swapped early on. Fender labelled the tremolo channel on its amps "Vibrato", while the Stratocaster's "tremolo arm" actually bends pitch — which is vibrato. Manuals are still confused today. In a DAW tremolo is usually tempo-synced, and with a hard square shape it shades into what dance producers call a trance gate.