A retaining ring is a circular fastener used to secure components on a shaft or in a housing. It fits into a groove and prevents parts from moving axially, ensuring they stay in place during operation. Retaining rings are commonly made from materials like steel or plastic and come in various sizes and designs, such as internal and external types. These rings are widely used in machinery, automotive applications, and electronics to maintain the alignment of parts. They are essential for the proper functioning of devices, as they help prevent wear and tear by keeping components securely positioned, contributing to overall reliability and safety.