Retaining rings, also known as snap rings or circlips, are circular fasteners that hold components together in mechanical assemblies. They typically fit into a groove on a shaft or in a bore (housing) to create a shoulder that prevents parts from dislodging. These rings are available in internal (for bores) and external (for shafts) configurations, and are commonly made of materials like steel, stainless steel, or oil-tempered wire.