Tuplets are when a beat is subdivided differently than the meter might indicate. The most common example is triplets, specifically eighth note triplets, where a beat normal subdivided by twos has three even subdivisions. This is shown with a bracket or the notes beamed together and a 3.
Quarter note triplets, also called drag triplets, are where the triplet takes up two beats to make three even notes.
“Send her my love,” by Journey has
subdivision triplets in the opening guitar part, and drag triplets at the opening of the chorus (1:05ish) https://www.youtube.com/watch?v=dKAxtgtiQaM (Upon further listening, I realized the opening is just eighth notes, drat.)
Triplets can then be subdivided more getting into sixes (sextuplets), or combinations of 3s and 6s:
In compound meter, the triple beat can be instead divided by twos and fours. These are called duplets and quadruplets. This is easier to show with notation, but could be either a tuplet notation or written out with a dot.
There are also subdivisions of 5 or 7 or whatever you can imagine. You can get fancy and say quintuplet or septuplet or whatever, but honestly most musicians I know say “5-tuplet.”