What is the difference between a male end piece and a female fitting?
The only thing that separates a male end piece from a female quick connector is where the fitting thread is located. On a male fitting, the thread is located on the outside, and on a female fitting, it is located on the inside.
The water treatment industry uses several other terms to describe fittings, like hose connectors and tube adapters. The terms connector and adapter really mean the same thing. If you want to be specific though, an adapter is typically a fitting that changes venue. On one end, there is a thread connection, and on the other, there is a stem adapter. However, they both are still connectors. The threaded side connects to other threads, and the stem side connects to tubing.