Pipe Thread - Male
In this category, tapered pipe threads like NPT, BSPT etc are used which are basically for the purpose of sealing without gaskets.

Pipe Thread - Female
Pipe Thread - Female is same as Pipe Thread - Male. Here too, tapered pipe threads such as NPT, BSPT, etc are used which is specifically for sealing without gaskets.

Straight Thread -
Male Straight pipe threads such as UNC, UNF, ASME, etc form Straight Thread - Male.

Straight Thread -
Female Straight Thread - Female also includes straight pipe threads such as UNC, UNF, ASME, etc.

Plain End
Plain End is used to insert into the bell end of the connecting pipe.

Bell / Socket / Flare
It is the end length of increased diameter into which a pipe end can be fitted.

Flange
There are two types of flanges, circular and square. These are used to connect fitting, typically via bolting or welding.

Compression Fitting
Compression fitting includes compression nut and ferrule by which it connects to a mating pipe.

Pipe Clamp End
Pipe Clamp End is designed in such a way so that it is attached to run on pipe or other fitting.

Barb / Rib
Barbs and ridges comprise fitting ends. They connect only non-rigid pipe or hose, or sometimes used with a clamped end.

Groove
Groove is for the installation of a coupling feature such as an o-ring or elastomeric seal.