A physical connection which is used primarily in 10base2 ethernet and professional/early video recorders as well as workstation monitors with separate cables for RGB.
BNC allows for two lines of a co-axial cable to be connected with a locking nut to reduce the likelyhood of the join separating. A BNC connector has a bayonet-type shell with two small knobs on the female connector which lock into spiral slots in the male connector when it is twisted on. Also known as RG58.
BNC is an Acronym for many many things:
BNC is also the name of an IRC 'bouncer' proxy program.
See also
Acronym for British National Corpus.
A 100 million word linguistic Corpus of British English widely used in computational linguistics. StuartYeates denies all knowledge of the BNC.
http://www.natcorp.ox.ac.uk/