A gasket consisting of a flat ring of rubber or plastic; used to seal a joint against high pressure WordNet 3.0 & Open English WordNet

An O-ring, also known as a packing or a toric joint, is a mechanical gasket in the shape of a torus; it is a loop of elastomer with a round cross-section, designed to be seated in a groove and compressed during assembly between two or more parts, forming a seal at the interface. Wikipedia

A gasket or seal with an O-shaped cross-section Wikipedia Disambiguation

Mechanical, toroid gasket that seals an interface Wikidata