Real Dictionary

cork
uncountable noun: Cork is a soft, light substance which forms the bark of a type of Mediterranean tree.

Cork in American English
county on the S coast of Ireland, in Munster province: 2,880 sq mi (7,459 sq km); pop. 283,000
made of cork
the light, thick, elastic outer bark of an oak tree, the cork oak (Quercus suber) of the beech family, that grows in the Mediterranean area: used for floats, stoppers, linoleum, insulation, etc.
to stop or seal with a cork
noun: the outer bark of an oak, Quercus suber, of Mediterranean countries, used for making stoppers for bottles, floats, etc

cork in British English
adjective: made of cork
noun: a county of SW Republic of Ireland, in Munster province: crossed by ridges of low mountains; scenic coastline. County town: Cork. Pop: 447 829 (2002). Area: 7459 sq km (2880 sq miles)
noun: the thick light porous outer bark of the cork oak, used widely as an insulator and for stoppers for bottles, casks, etc

cork in Hospitality
noun: A cork is a piece of cork or plastic that is pushed into the opening of a bottle to close it.