A set in Okey is three or four tiles of the same number in different colours.

For example, a red 7, a black 7 and a blue 7 form a valid set. Each colour can appear only once in a set, so you cannot use two red 7s together. A set can hold three or four tiles because there are four colours in play. The okey joker may replace a missing colour. Combining runs and sets to cover all 14 tiles, plus one tile left to discard, is how you finish a hand.