Threat detection is the practice of analyzing the entirety of a security ecosystem to identify any malicious activity that could compromise the network. If a threat is detected, then mitigation efforts must be enacted to properly neutralize the threat before it can exploit any present vulnerabilities.
Getting breached is a nightmare scenario, and most organizations that prioritize their information will put smart people and technologies to work as a defensive barrier against anyone who might try to cause trouble. This is why we exist.