Washer, Plastic Washer, UHWPE washer, PTFE washer, PMMA washer, Compressed fiber gasket:A gasket is a mechanical seal which fills the space between two or more mating surfaces, generally to prevent leakage from or into the joined objects while under compression
Fiber, Sealing washer:A washer is a thin plate (typically disk-shaped) with a hole (typically in the middle) that is normally used to distribute the load of a threaded fastener, such as a screw or nut.
Washer also called as static seal. It is a mechanical element use to prevent the leakage of fluid between the two components which are static or doesn't have relative motion. While Oil Seal also called as dynamic seal is use to prevent leakage of fluid between two components having relative rotary or sliding motion.
A washer is primarily used to seal two mating surfaces. It prevents leakage of fluids. Washers on the other hand are used primarily to spread pressure evenly, and are used in places of high vibration.