An O-ring is a circular, doughnut-shaped seal made from flexible materials like rubber or silicone. It is designed to fit into a groove and create a tight seal between two surfaces, preventing the leakage of fluids or gases. O-rings are commonly used in various applications, including automotive engines, plumbing, and industrial machinery. These seals work by compressing when two parts are joined, filling the gap between them. This compression helps maintain a barrier against pressure and contaminants. O-rings are available in different sizes and materials, making them versatile for many industries, including aerospace, manufacturing, and medical devices.