A pipe fitting is a fitting used to connect pipe segments, that is placed at a junction or transition in a piping system and may be used to change flow characteristics such as direction and flow rate. In this instance valves are not classified a pipe fittings, they are classified as valves.
A pipe obstruction fitting is a pipe fitting with typically two ports used to obstruct or restrict flow between the connected elements (e.g. screen, perforated plate, etc.).