Cyberspace refers to a (virtual) reality within the world's computers and computer networks. Cyberspace is a common theme in science fiction.
The word "cyberspace" was coined by William Gibson, the Canadian science fiction writer, in his 1984 bestseller Neuromancer.
While cyberspace should not be confused with the real Internet, the term is often used simply to refer to objects and identities that exist largely within the computing network itself, so that this Wikipedia, for example, might be metaphorically said to "exist in cyberspace." According to this interpretation, events taking place on the Internet are not therefore happening in the countries where the participants or the servers are physically located, but "in cyberspace". This becomes a reasonable viewpoint once distributed services (e.g. Freenet) become widespread, and the physical identity and location of the participants become impossible to determine due to anonymous or pseudonymous communication. The laws of any particular nation state would therefore not apply.
The show Digimon is set in a version of cyberspace called the "digital world". The digital world is a parallel universe made up of data from the internet. Simliar to cyberspace, except that people could actually enter this world instead of just being on a computer.
"Meatspace" is a term coined later as an opposite of "cyberspace".
See also
Cyberpunk, Cyberculture, Internet art, Noosphere, cyber law, crypto-anarchism, cipherspace