Seal types refer to the various categories of seals used in different applications, primarily for preventing leaks in machinery and plumbing. Common types include O-rings, gaskets, and mechanical seals. Each type is designed to fit specific shapes and sizes, ensuring a tight seal to keep fluids or gases contained. Different materials are used to create these seals, such as rubber, silicone, and metal, depending on the environment and pressure conditions. For instance, gaskets are often used in engines, while O-rings are common in hydraulic systems. Choosing the right seal type is crucial for optimal performance and durability.