A run is consecutive numbers in one colour, while a set is the same number in different colours.

For example, blue 5-6-7 is a run because the colour stays the same and the numbers climb in order. A set would be 5s in three different colours, such as red, black and blue 5. Runs can grow long along a single colour; sets are capped at four tiles because there are only four colours. You finish a hand by covering all your tiles with a mix of these two group types.