A triplet is a group of three evenly spaced notes sung within one beat. Eighth note 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 sung with one third of a beat each. Triplets are easy to understand once you have heard them played.
Triplets sound great when combined with the notes of the Blues scale as shown in the following example. Notice that the note F# is used here instead of Gb. This can be done because the two notes are enharmonically the same. The degree is still the flattened fifth (b5).