Adapter is any fitting that adapts one type of connection to another. Such as a PVC slip connection to a threaded connection, or change a pipe thread fitting to a garden hose thread, and even connect poly tubing to a threaded pipe or hose connection.

Bushing is a fitting that fits inside a pipe fitting or another threaded fitting and connects another pipe section or threaded fitting inside of the bushing fitting.

Cap closes the end of a run of pipe, tubing, or hose often fitting over the pipe.

Coupler, often called a coupling or connector, is a straight fitting used to connect two sections of pipe, tubing, or hose together.

Cross is a fitting with four outlets running at 90 degrees of each other.

Elbow is a fitting that creates a turn in the pipe, tubing, or hose.

45 90 3-way

Nipple is a straight coupler or riser with male connections or threads at both ends.

Close Nipple Riser Reducing

Plug closes an opening, frequently the end of a threaded fitting.

Another type is a Goof Plug, which can also be used to close a hole that was punched in your poly tubing that is no longer needed.

Reducer is any fitting that connects pipe, tubing, or hose of one size to another smaller (or larger) size pipe, tubing, or hose.

Saddle/Snap Tee can be used to add a new line off an already installed piping system. The tee fitting snaps over the pvc pipe and then a hole must be drilled into the pipe to open a water passage for the branch pipe. A PVC saddle/snap fitting is solvent welded onto the pipe prior to drilling the hole.

Something like the Blu-Lock Saddle Tap Tee does not require glue or cement, just a snap and a twist of the tap.

Socket is a PVC slip fitting that fits over the pipe of the same nominal size. Slip fittings require solvent welding. Often referred to as the female end.

Spigot is a PVC slip fitting that fits inside a slip socket fitting. Often referred to as the male end. Slip fittings require solvent welding.

Socket/Spigot is a fitting that will function as either. As a socket it fits over the appropriate size PVC pipe and as a spigot it will fit inside the pvc fitting of the next larger pipe size. Just remember not all PVC slip fittings can function as both a socket and spigot.