In music theory, you will find these terms: Irrational rhythm, artificial division, or abnormal divisions. Here we will use the term of tuplet. All these terms are applied to rhythms that involves dividing the beat into a different way from that usually permitted by the time signature.
For example, with a time signature, you can only divide each by beat by a multiple of 2, so 1 beat can contain 2 , 4 , 8 , 16 , or 32 . Normally, in such a time signature, you can't divide the beat by 3, 5, 7, or 9, but the only way to do it is to use tuplets.
Most common tuplets: Triplets and duplets
Learn all about triplets: A triplet is a tuplet that permit to divide the beat (or more than 1 beat) by 3 in simple meters. Learn how to play triplets with our examples. Read this article
Learn all about duplets: A duplet is a tuplet that permit to divide the beat (or more than 1 beat) by 2 in compound meters. Learn how to play duplets with our examples. Read this article