A security alert is a notification generated by a security tool when it detects a potential issue. The nature of the alert depends on its source. Antivirus software, for instance, generates alerts when it detects malware; an IDS generates alerts when it detect suspicious network traffic. In large-scale cybersecurity environments, specialized software is used to collect these alerts and display them all in one place.
After receiving an alert, analysts will investigate it to determine what happened and what to do about it. The response to some alerts may be quite straightforward, such as deleting a malicious file that a user accidentally downloaded. On the other hand, an alert about suspicious network activity may indicate that an attacker has gained access to the network — in this case, the security team must identify how the attacker was able to gain access in order to terminate that access and prevent further breaches.