Vibrato
A periodic wobble in pitch — what singers do with their throat and violinists with their hand.
On a synth an LFO is routed to oscillator pitch, and the mod wheel — MIDI CC 1 — controls how much. As an effect on finished audio it is built from a short delay line whose length is modulated: as the delay shrinks, the sound plays back slightly faster and pitch rises; as it grows, pitch falls. That is exactly the machinery of a chorus, minus the dry signal.
The Leslie speaker on Hammond organs got there mechanically, with a spinning horn and the Doppler effect. The difference from tremolo is easy to state and apparently hard to remember: vibrato moves pitch, tremolo moves volume. The guitar industry has been mixing them up for seventy years.