Seals are mechanical devices used to prevent leakage or contamination between two surfaces, ensuring the integrity of enclosed systems. They come in various forms, including O-rings, gaskets, lip seals, and mechanical seals, tailored to specific applications and environments. Seals are made from materials like rubber, silicone, metal, or composite materials, selected based on factors such as temperature, pressure, chemical compatibility, and mechanical stress. Common applications include automotive engines, hydraulic systems, pumps, valves, and industrial machinery. Proper installation, maintenance, and material selection are essential for optimal sealing performance and system reliability.