A rubber O-ring is a type of mechanical seal that is commonly used to prevent the leakage of fluids or gases in various applications. It is a circular-shaped ring made from rubber or other elastomeric materials, and its name comes from its "O" shape when viewed in cross-section.

Rubber O-rings work by creating a tight seal between two parts, preventing the flow of fluids or gases between them. They are typically used in applications where high pressure or vacuum conditions are present, such as in hydraulic systems, pneumatic systems, and engines.

Rubber O-rings come in various sizes and materials, including nitrile, silicone, Viton, and EPDM, each with different properties and suitable for specific applications. They are designed to fit snugly in a groove or recess between two parts, compressing and forming a seal when the two parts are joined together.

O-rings are easy to install and replace, making them a popular choice for sealing applications in various industries. However, they may need to be replaced periodically to ensure continued effective sealing performance.