It describes such phenomenon – activity, process, object – whose operation, target or result is equivalent to the real life's phenomenon, however there is a lack of the typical appearance or dimension of the object.
Namely, the virtual is the potential, possible status of the phenomenon, in case there is the possibility to become real (Gilles Deleuze 1966).

Kommunikációtudományi Nyitott Enciklopédia retrieved 02.11.2014
Chandler, Daniel–Munday, Rod (2011): A Dictionary of Media and Communication. Oxford University Press. Oxford. 452. p. See the Online Edition
University of Chicago retrieved 02.11.2014