An eighth note triplet is a group of three evenly spaced notes played 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. Eighth note triplets are played with one third of a beat each. Triplets are easy to understand once you have heard them played. triplets are easy to understand once you have a feel for how they are played.
A good way to become familiar with the triplet rhythm is to apply it to the Blues scale. The result should sound familiar to you. The scale shown here is the C Blues scale but it is important to practice the Blues scale in all keys using the triplet rhythm.
It is also a good idea to practice arpeggios with a triplet rhythm. Here is an F7 arpeggio played over two octaves using triplets.