The interdependent network of information technology infrastructures that includes the Internet, telecommunications networks, computers, information systems, industrial control systems, networks, and embedded processors and controllers.
Sources:
CNSSI 4009-2022 from NSPM-13

  A global domain within the information environment consisting of the interdependent network of information systems infrastructures including the Internet, telecommunications networks, computer systems, and embedded processors and controllers.
Sources:
NIST SP 800-30 Rev. 1 under Cyberspace from CNSSI 4009
NIST SP 800-39 under Cyberspace from CNSSI 4009

  The interdependent network of information technology infrastructures that includes the Internet, telecommunications networks, computer systems, and embedded processors and controllers in critical industries.
Sources:
NIST SP 800-160 Vol. 2 Rev. 1 from NSPD-54/HSPD-23, CNSSI 4009-2022
NIST SP 800-53 Rev. 5 from CNSSI 4009-2022

  the complex environment resulting from the interaction of people, software and services on the Internet by means of technology devices and networks connected to it, which does not exist in any physical form.
Sources:
NISTIR 8074 Vol. 2 under Cyberspace