Also, an American
football term for a grouping of a team's predesigned plays, often in
book form.
Each play is drawn graphically (with X's and O's representating the individual players, and lines and arrows emanating from each player, showing where each player should go).
Plays are usually given strange-sounding code names which the quarterback or defensive captain can call and everyone on his team knows what their assignments are for the upcoming play.
Football video games similarly use playbooks, where the player scrolls through the playbook and chooses a play to run.
An example of football plays/playbook can be found at http://www.football.com/playbook/index.shtml
To a lesser degree, basketball also uses the concept of predesigned plays and playbooks.