Why should we always divide notes in two? Why would one not be able to divide it in 3 or 5? Let's mess with the rules.
Tuplets express an irregular rhythm — dividing a note in three where it would normally be divided in two, or the opposite.
Simple examples
Triplet
3 notes played in the place of 2. Ratio: 3:2.
Quintuplet
5 notes played in the place of 4. Ratio: 5:4.
Sextuplet
6 notes played in the place of 4. Ratio: 6:4.
Tuplets with Flat
Flat supports: 3/2, 5/4, and 6/4. Try them in Flat!