For each one of the four categories of features - color, number, shape, and shading - the three cards must display that feature as either a) all the same, or b) all different.

In the game, certain combinations of three cards are said to make up a 'set'. a card with three striped green diamonds) appears as a card precisely once in the deck. Each possible combination of features (e.g. The deck consists of 81 unique cards that vary in four features across three possibilities for each kind of feature: number of shapes (one, two, or three), shape (diamond, squiggle, oval), shading (solid, striped, or open), and color (red, green, or purple). Set (stylized as SET or SET!) is a real-time card game designed by Marsha Falco in 1974 and published by Set Enterprises in 1991. Visualization, logical reasoning, ability to focus

These cards each have a unique number, symbol, shading, and color, and are thus a 'set'.