Definition - What does O-Ring mean?
O-Ring, also known as a toric joint is a packing or sealing material used to seal two or more mechanical equipment parts. The ring acts like a mechanical gasket which has the shape of torus, and a loop of elastomer with a rounded cross section. It can be seated in a special designed groove for them on the edges of two equipment parts that need to be joined with a high-end sealing.
Petropedia explains O-Ring
An O-ring can be used either in static or dynamic applications where there is relative motion between the joining parts. For example, it can be used in rotating pump shafts and hydraulic cylinder pistons. The ring is an important part in any mechanical equipment as it provides a permanent and tight seal between two metal parts. Apart from this it is, easy to manufacture, cost-efficient, easily available in the market, reliable and can be simply mounted on a seal slot provided on the parts. One good property of such seal is that it can seal thousands of psi pressure.