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 from NSPD-54/HSPD-23
NIST SP 1800-10B under Cybersecurity from CNSSI 4009-2015, NSPD-54/HSPD-23
NIST SP 1800-25B under Cybersecurity from CNSSI 4009-2015, NSPD-54/HSPD-23
NIST SP 1800-26B under Cybersecurity from CNSSI 4009-2015, NSPD-54/HSPD-23
NIST SP 800-160 Vol. 2 Rev. 1 from CNSSI 4009-2015
NIST SP 800-37 Rev. 2 from OMB Circular A-130 (2016)
NIST SP 800-53 Rev. 5 from OMB Circular A-130 (2016)
NIST IR 8401 from NIST SP 800-53 Rev. 5
NISTIR 7621 Rev. 1 under Cybersecurity from CNSSI 4009-2015

  The process of protecting information by preventing, detecting, and responding to attacks.
Sources:
NIST SP 800-160 Vol. 2 Rev. 1 from NIST Cybersecurity Framework Version 1.1
NIST Cybersecurity Framework Version 1.1 under Cybersecurity
NISTIR 8183 under Cybersecurity from NIST Cybersecurity Framework Version 1.1, NIST Cybersecurity Framework Version 1.0
NISTIR 8183 Rev. 1 under Cybersecurity from NIST Cybersecurity Framework Version 1.1
NISTIR 8183A Vol. 1 under Cybersecurity from NIST Cybersecurity Framework Version 1.1
NISTIR 8183A Vol. 2 under Cybersecurity from NIST Cybersecurity Framework Version 1.1
NISTIR 8183A Vol. 3 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 Rationale: Term has been replaced by the term “cybersecurity”.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)

  The ability to protect or defend the use of cyberspace from cyber attacks.
Sources:
NISTIR 8170 under Cybersecurity from CNSSI 4009

  the prevention of damage to, unauthorized use of, exploitation of, and—if needed—the restoration of electronic information and communications systems, and the information they contain, in order to strengthen the confidentiality, integrity and availability of these systems.
Sources:
NISTIR 8074 Vol. 2 under Cybersecurity

  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 from NIST SP 800-53 Rev. 5 - [adapted]