Stricture is the extent to which the oral tract is constricted. The following diagram is ordered with the greatest "degree" (or "rank order") of stricture at the top and the least degree of stricture at the bottom. The greatest degree of stricture is the "stop" with complete closure or constriction of the oral cavity at some point.
Note that stricture specifically relates to oral cavity constriction and ignores the state of the nasal cavity (ie. whether the velum is open or closed).