Cybernation is most often used to refer to the control of a system, especially an industrial/manufacturing system, by computer. It is a portmanteau of cybernetic and automation.
Occasionally, cybernation, or sometimes CyberNation, is used to refer to a large on-line community or the entirety of internet users as a group. Usually it is a vague combination of the two -- e.g., a statement like "policing the cybernation" would suggest that it involves all the internet, but in fact would in practice be limited by national jurisdictions; in other cases it is in fact limited by certain skillsets (e.g., coding ability) or language.
Cybernation is also the 6th book in Tom Clancy's Net Force series.