What is the term for having information about threats and threat actors that helps mitigate harmful events that would otherwise compromise networks or systems?

Definitely Threat Intelligence
Cyber threat intelligence (CTI) is knowledge, skills and experience-based information concerning the occurrence and assessment of both cyber and physical threats and threat actors that is intended to help mitigate potential attacks and harmful events occurring in cyberspace.

Indicator of compromise (IoC) in computer forensics is an artifact observed on a network or in an operating system that, with high confidence, indicates a computer intrusion.

Ref: https://en.wikipedia.org/wiki/Cyber_threat_intelligence