In this guitar lesson, you’ll learn how to play triplets.  (It is advised that you familiarize yourself with time signatures before you go through this lesson.)  A triplet is essentially three notes in the place of two.  It is used in many styles of music including blues, rock, jazz and country. 

By rewriting the time signature, you can play triplets in these popular meters:

3/4 (used for waltzes, minuets, scherzi, country & western ballads, sometimes used in pop.)
3/8 (used for the same styles as 3/4 but usually suggests higher tempo or shorter hypermeter.)
9/8 (“compound triple time”, used in triple (“slip”) jigs, otherwise occurring rarely.)

Other rewritings of time signatures are also possible.  It’s up to your imagination!