Positioning is the concept of what possible moves or plays exist at any given time.
The Big Model[]
The Big Model talks about positioning as a Character Component. That is, behavioral, social, and contextual statements about a character. This is a broadly applicable description, but assumes as context that "the character" is the focus of possibilities of play.
Vincent Baker and Emily on positioning[]
Vincent Baker wrote a response to Emily's analysis on the matter. Discarding assumptions about the player-GM split, number of players, player roles and stances, and so forth, Baker formulated the following definition:
A player's position is the total set of all of the legitimate gameplay options available to her at this moment of play. Positioning refers to the various factors and processes, including in-fiction, cue-mediated, and interpersonal, that determine a player's position.
This definition does not itself distinguish between options that are free, that is, available to the player in an absolute sense, and those that are open, that is, what options can be played in the moment. See also initiative.