guitarists mistake tremolo for vibrato and vice
versa. Even worse, the famous tremolo bar on guitars actually creates a vibrato effect.
In this article the difference is visualised and audiolised.
Varying frequency (pitch or tone height) over time.
A 440 Hz tone with 6 Hz vibrato effect:
Varying amplitude (volume) over time.
A 440 Hz tone with 6 Hz tremolo effect: