An eighth note triplet is a group of three evenly spaced notes played within one beat. Triplets are indicated by three eighth notes grouped together by a bracket (or a curved line) and the numeral 3. The eighth note triplets are played with one third of a beat each. Triplets are easy to understand once you have heard them played.
Here is a triplet variation on the Blues riff you learned in Lesson 6. This one is played cross harp in the key of G.
This one is a Blues intro riff also played cross harp in the key of G. Listen to how effectively this triplet rhythm works with the other instruments.