Most musical notes divide a beat neatly by some factor of two. But every now and then, a piano composer wants to divide a beat into more than two eighth notes but less than four sixteenth notes. That means playing three notes per beat, aptly called a triplet.
The most common triplet pattern is the eighth-note triplet, which looks like three beamed eighth notes. To help you spot these triplets quickly, composers add a little number 3 above (or below) the beam. A popular variation on this triplet pattern is the quarter-eighth triplet, which looks like (get this) a quarter note and an eighth note but with a little bracket and a number 3.
To count triplets, tap your foot and say “1 trip-let, 2 trip-let” or “choc-o-late” for every beat. The most important point is to divide the beat into three equal parts so each syllable gets its fair share.
You can make triplets using other note values, too, but you probably won’t have to play them until you start jamming with your local drum circle. It’s worth remembering, though, that with any triplet rhythm, 3 = 2: Three quarter-note triplets equal two quarter notes (two beats), and three sixteenth-note triplets equal two sixteenth notes (half a beat). You play three notes (equally) in the time you would normally play two notes of the same value.