A clip is a cheap, disposable piece of sheet metal that is used to load a magazine or a cylinder. The magazine is the ammunition reservoir for a repeating firearm.
You can not have a repeating firearm without a magazine system of some sort, but you can, in most cases, load the magazine without a clip.
The word "clip" is commonly (though incorrectly) used as a synonym for magazine.
Types of clips
The other style is the "charger", commonly referred as a "stripper clip". With this item, the clip is mounted in machined grooves in the receiver or in an adapter mounted on the rear of the removable magazine, and the rounds pushed, or "stripped" into the magazine. The charger is then removed from the receiver, or magazine, and tossed.
The original "en-bloc" style was developed by Mannlicher of Austria in 1880's.
Probably, the most famous use of this system was the M1 Garand. On this firearm, the clip and ammunition is loaded into the weapon at the same time. After the last round in the clip is fired, it is automatically ejected, clearing the weapon for the next loading.
Moon clips are star ring-shaped pieces of metal used to hold rounds for loading into a cylinder. Unlike a revolver speed loader, the moon clip also stays in the cylinder, ejecting with the casings when reloading. Moon clips also aid in the ejection of rounds, and as a result, they are typically loaded into revolvers that use rimless cartridges.
As the name suggests, a half-moon clip is essentially half of a moon clip. It is a semi-circular ring and designed to hold a half cylinder's worth of ammunition.