Definition of "triplet"

A set of three, particularly

1. (music) A group of three notes played or written where two notes would ordinarily be; a form of tuplet.  examples

2. (physics) A triquark.  examples

3. (physics) A quantum state with three allowed projections for the spin.  examples

4. A constructed gem consisting of a thin slice of natural opal sandwiched between a clear glass or quartz top and a synthetic or stone backing that enhances the colour of the opal.  examples

One of a group of three, particularly

1. One of a group of three siblings born at the same time to the same mother.  examples