Imagine a boy playing with a ball. He kicks the ball against a wall, and the ball bounces back to him. He stops the ball with his foot and kicks it again. By engaging in this kind of play, the boy learns to associate certain movements of his body with the movements of the ball in space. We could call this associative play.
Now imagine that the boy is waiting for a friend. The friend appears, and the two boys begin to walk down a sidewalk together, kicking the ball back and forth as they go. Now the play has gained a social dimension; one boy's actions suggest a response, and vice versa. You could think of this form of play as a kind of improvised conversation, where the two boys engage each other using the ball as a medium. This kind of play has no clear beginning or end; rather, it flows seamlessly from one state into another. We could call this streaming play.
Now imagine that the boys come to a small park, and that they become bored simply kicking the ball back and forth. One boy says to the other, "Let's take turns trying to hit that tree. You have to kick the ball from behind this line." The boy draws a line by dragging his heel through the dirt. "We'll take turns kicking the ball. Each time you hit the tree you get a point. First one to five wins." The other boy agrees and they begin to play. Now the play has become a game; a fundamentally different kind of play.