"Play" cannot really be defined with a single definition. Many different aspects go into it, and all of them piece together the mentality that drives the reasoning behind “play” in the first place. These different aspects are:

Self-Chosen and Self-Directed
This statement essentially means that free will is an essential part of playing. Players should be able to choose whether or not they want to participate in the play-time activity. They should also be able to decide how they play. When playing involves a group of people and the activity needs a leader to function, the leader can only be one if the other players involved accept them as such. Any member of the group should be able to suggest rules, and the only rules that should be active are the ones agreed upon by every player. The ability to quit the game at any time gives players the power to keep a leader who tries to abuse his or her power in check.

Intrinsically Motivated
Basically, “play” is defined by a player as something that they do because they enjoy the activity, not because they care about receiving a possible reward in the end. For example, people who work jobs that they don’t like only do it because they want to earn money—they only do it because there is a reward to be received in the end. They do as little as they possibly can to get by in their job because they do not find any interest in it. On the other hand, people who work their dream job do not care about receiving a reward in the end because the activity of said job is interesting to them. They enjoy giving it all of their focus and attention because it makes them happy—it resembles “play.”

Rules that Leave Room for Creativity
While the act of play emphasizes free will, it is not a structureless activity. The rules of play need to be followed in order for play to be what it is, but these rules never entrap the player because they were created by them—in other words, the player follows the rules only because they like and accept them. They themselves create the structure that they work in, so to say.

Play is Imaginative
Play will also force the player to mentally remove themselves from the real world in some way shape or form. This separation is imagination, and play requires this because it is not bound by the physical laws of reality, but by the mind of the player (again, the idea that the player follows the rules of play only because they want to rather than because they have to).

Play Makes One Alert Without Stress
The final aspect of play originates from the other four. Play makes the player alert to their own behavior because they want to make sure that they are following the rules of whatever activity they are involved in. But, because they are in full control of whatever it is that they want to do, they are free of whatever stress or pressure that would normally come with breaking real-world rules.