A tremolo arm, tremolo bar, vibrato bar or whammy bar is a lever attached to the bridge and/or the tailpiece of an electric guitar or archtop guitar to enable the player to quickly vary the tension and sometimes the length of the strings temporarily, changing the pitch to create a vibrato, portamento or pitch bend effect. Instruments without this device are called hard-tail.
The tremolo arm is the most common type of vibrola unit. The term vibrola is also used by some guitar makers to describe their particular tremolo arm designs; see vibrola.
The tremolo arm began as a mechanical device for more easily producing the vibrato effects that blues and jazz guitarists had long produced on arch top guitars by manipulating the tailpiece with their right hand. However it has also made possible many sounds not available by this technique.
Since the appearance of mechanical tremolo arms in the 1950s, artists such as Jimi Hendrix, Steve Lukather, Joe Satriani, Eddie Van Halen and many surf music bands have used the tremolo to great effect, and the effects they created using it have become a recognised part of many styles of electric guitar.