Vibrato refers to an intentional wavering of pitch to make notes more expressive. There are three basic ways to get vibrato on a guitar. The most common method involves bending the string back and forth across the fingerboard. This can also be done to multiple strings to embellish riffs.

A more subtle effect is produced by pivoting your finger along the length of the string like players of fretless instruments such as the violin.

The third method for producing vibrato involves a tremolo arm which has the advantage of being able to add vibrato to open strings and chords. The two variables are depth and speed so experiment with the amount you move the string and the speed at which you do it. You can also apply vibrato to a bend.

Example 7a