The term cyberspace was coined by William Gibson; who would later claim that the term was essentially "meaningless", and could be applied to any sci-fi/cybernetic "musing". Other notable sci-fi/computing "gurus" believe that the term refers to those things which occur within the confines digital data transmissions, but which bare no relation to the technology itself.
Historically, the term has been used to describe a number of technological and scientific innovations; for example, it's been used to describe a visually navigable computer world, which was attempted by technologies such as virtual reality in the early 1990's. As the term was coined by William Gibson in the early 1980's - a time when home computing was just beginning to capture the imagination of the populace at large - it's perhaps not surprising that sci-fi authors had difficulty grappling with how the technology would impact upon humanity into the future, and therefore needed a somewhat "meaningless" term like cyberspace.
The term cyberspace is also used to describe events within the Internet; "such and such occurred in cyberspace" is a common phrase used by media outlets to describe an event which originated on the Internet: such as a leaked document on wikileaks. As time has passed, it is probably fair to suggest that the usage of the word "cyberspace" appears to be used less in conjunction with the Internet. Usage of cyberspace to relate to Internet "doings" probably reached it's zenith in the mid to late 1990's; other terms have tentatively be used instead: most recently (2012) "the cloud".