According to Caillois in Man, Play, and Games, play is defined as such:

1. Free: in which playing is not obligatory; if it were, it would at once lose its attractive and joyous quality as diversion;
2. Separate: circumscribed within limits of space and time, defined and fixed in advance;
3. Uncertain: the course of which cannot be determined, nor the results attained beforehand, and some latitude for innovations being left to the player’s initiative;
4. Unproductive: creating neither goods, nor wealth, nor new elements of any kind; and, except for the exchange or property among the players, ending in a situation identical to that prevailing at the beginning of the game;
5. Governed by rules: under conventions that suspend ordinary laws, and for the moment establish new legislation, which along counts;
6. Make-believe: accompanied by a special awareness of a second reality or of a free unreality, as against real life.