Prevention of damage to, protection of, and restoration of computers, electronic communications systems, electronic communications services, wire communication, and electronic communication, including information contained therein, to ensure its availability, integrity, authentication, confidentiality, and nonrepudiation.
Sources:
CNSSI 4009-2015 under cybersecurity from NSPD-54/HSPD-23
NIST SP 800-160 Vol. 2 Rev. 1 under cybersecurity from CNSSI 4009-2015
NIST SP 800-37 Rev. 2 under cybersecurity from OMB Circular A-130 (2016)
NIST SP 800-53 Rev. 5 under cybersecurity from OMB Circular A-130 (2016)
NIST IR 8401 under cybersecurity from NIST SP 800-53 Rev. 5

  The process of protecting information by preventing, detecting, and responding to attacks.
Sources:
NIST SP 800-160 Vol. 2 Rev. 1 under cybersecurity from NIST Cybersecurity Framework Version 1.1

  Measures and controls that ensure confidentiality, integrity, and availability of the information processed and stored by a computer. Rationale: Term has been replaced by the term “cybersecurity”.
Sources:
CNSSI 4009-2015 under computer security (COMPUSEC) from NSA/CSS Manual Number 3-16 (COMSEC)

  Prevention of damage to, protection of, and restoration of computers, electronic communications systems, electronic communications services, wire communication, and electronic communication, including information contained therein, to ensure its availability, integrity, authentication, confidentiality, and nonrepudiation. For example, PNT data is generated by cyber systems. Protection of the devices and systems used to generate PNT data should be considered part of cybersecurity.
Sources:
NIST IR 8323r1 under cybersecurity from NIST SP 800-53 Rev. 5 - [adapted]