Well, to the extent that Wikipedia can be trusted:
https://en.wikipedia.org/wiki/Cyberspace
Quoting:
derived from the Ancient Greek κυβερνήτης (kybernētēs, steersman, governor, pilot, or rudder), a word introduced by Norbert Wiener for his pioneering work in electronic communication and control science.
And then further down (interesting that the original use of "cyberspace" had nothing to do with an internet of any sort, or even the global telephone network):
The term “cyberspace” first appeared in the visual arts in the late 1960s, when Danish artist Susanne Ussing (1940-1998) and her partner architect Carsten Hoff (b. 1934) constituted themselves as Atelier Cyberspace. Under this name the two made a series of installations and images entitled “sensory spaces” that were based on the principle of open systems adaptable to various influences, such as human movement and the behaviour of new materials.[6]
Atelier Cyberspace worked at a time when the Internet did not exist and computers were more or less off-limit to artists and creative engagement. In a 2015-interview with Scandinavian art magazine Kunstkritikk, Carsten Hoff recollects, that although Atelier Cyberspace did try to implement computers, they had no interest in the virtual space as such:[6]
To us, ‘cyberspace’ was simply about managing spaces. There was nothing esoteric about it. Nothing digital, either. It was just a tool. The space was concrete, physical.
And then further down:
The term "cyberspace" first appeared in fiction in the 1980s in the work of cyberpunk science fiction author William Gibson, first in his 1982 short story "Burning Chrome" and later in his 1984 novel Neuromancer.[8] In the next few years, the word became prominently identified with online computer networks. The portion of Neuromancer cited in this respect is usually the following:[9]
Cyberspace. A consensual hallucination experienced daily by billions of legitimate operators, in every nation, by children being taught mathematical concepts... A graphic representation of data abstracted from the banks of every computer in the human system. Unthinkable complexity. Lines of light ranged in the nonspace of the mind, clusters and constellations of data. Like city lights, receding.