Few parts of a guitar, if any, have as many different names and terms used to describe it as the tremolo arm. The tremolo arm is an adjustable lever which is connected to the bridge of the guitar. By moving this arm or lever, the bridge is raised and lowered, and by raising or lowering the bridge, the strings are themselves raised and lowered. This slightly stretches the strings, resulting in a change of pitch, and adjusting this up and down quite rapidly gives rise to the tremolo effect, or rapid pitch bending.
Some of the names commonly given to the tremolo arm include the tremolo bar, the sissy or wang bar, the slam or whammy handle, and also the whammy bar. Both the whammy handle and whammy bar are slang terms used for a long time, and have since given rise to the idea of a 'whammy', being a slang term itself to describe the action or effect of a rapid change in pitch, and in some cases there are now electronic devices or facilities built in tot eh amplification equipment connected to electric guitars that replicate the effect of a whammy without the physical use of a tremolo bar to achieve it, instead adjusting the note electronically. In fact, the word tremolo, or rather its use within the context of this electric guitar effect, can be traced back to one of the earliest leading designers of electric guitars, Leo Fender.
Although he was responsible for a huge amount of excellent design development where the electric guitar is concerned, it was also Fender who gave rise to the popular misunderstanding of the term tremolo, and in particular the confusion between what tremolo really means, and the word vibrato. Technically, the term vibrato refers to the effect of a change in pitch either up or down the scale, and the word tremolo actually refers to a change in volume. Both of these terms have long historic roots in music notation and its Latin origins, but thanks to Leo Fender, what should be referred to as a vibrato arm is now referred to by almost any other name.
Today, most designers and manufacturers of electric guitar and electric guitar related equipment reverse the meanings of these two words to avoid confusion within the world of the electric guitar, and so vibrato still refers to a change in volume, whilst tremolo still refers to a change in pitch. However, in other musical circles you will find that these words refer to each others' meanings. Although the most common form of a tremolo arm is the traditional lever attached to the bridge, there are two other main types of tremolo mechanism, in particular the Bigsby and the B-Bender. The Bigsby is a mechanical vibrato effect which involves a metal bar being placed some way up the neck of the guitar.
The strings are wrapped around this bar, and the player can adjust the pitch, in other words, creating the tremolo effect, by rotating this bar. The rotation of the bar causes the change in tension and therefore pitch of the strings, resulting in a similar effect. The B-Bender is quite different, and the mechanism usually resides inside the guitar, and this, as the name suggests, is connected solely to the B string, so that this one string alone has the tremolo effect, giving rise to a sound similar to that of a pedal steel guitar.
Of course, not all electric guitars have this physical mechanism, although many do, and in some cases, the tremolo arm can be added later, but in all cases, whether the effect is physically present or not, the result can still be achieved electronically by using the amplification equipment, the only downside being of course that it is less tactile and more distant from the actual playing of the instrument.