Further info
There is also the "half moon" (3rnd) and "full moon" (6rnd) clips designed to allow the use of rimless ammo (.45acp) in DA revolvers. I even have a couple dozen or so 2nd clips for the same purpose.
Half moon clips made their first appearance (that I know of) with the 1917 Colt and S&W .45 ACP revolvers made for WW I. The DA extractor normally pushes against the case rim, but the rimless .45acp had nothing to push against. So cases had to be poked out one at a time with a stick, or rod, which really slows down the reloading.
The solution was the half moon clip, or .45 Auto Rim ammo. The half moon clip (named because it resembles a half moon, a half circle) is a flat piece of spring steel that holds 3 rounds in proper spacing to be inserted into the cylinder. The rounds stay in the clip, the fired cases and the clip are extracted together. 2 half moon clips is a very fast way to load and reload a DA revolver. This idea has been used in some modern guns as well, for the reason of its speed and simplicity. Full moon clips are complete circles, holding 6 rounds, and working just like 2 half moon clips, only being one unit, it is even faster. Moon clips will only work in guns that have been made for, or modified to accept them. In an unmodified gun, the added thickness of the clips prevents the cylinder from closing, or if it closes, it normally can't turn.
Auto Rim brass was made to be used in the guns that used moon clips, without the clips. .45AR brass has a very thick rim, equaling the thickness of the .45ACP ammo and the clips.
In mechanical jargon, a clip is a something that retains or fastens something. In guns, clips do the same job for some parts (and may be called retaining clips, or snap rings, or something similar). When referring to ammo, clips hold ammo together. Many designs have the ammo removed for feeding/firing, (stripper, enbloc) but some (like moon clips) do not.