Indicators of Attack (IoA) refer to observable behaviors or artifacts that suggest a security breach or ongoing attack.
When internal hosts communicate with countries outside the business range, it may indicate data exfiltration or command-and-control communication to an external threat actor.
Unlike Indicators of Compromise (IoC) which indicate that a system has already been compromised, IoAs are often used to identify malicious activity in its early stages.
Monitoring for unusual outbound connections is a crucial aspect of detecting advanced persistent threats (APTs) and other sophisticated attacks.
Reference
Difference Between Indicators of Compromise and Indicators of Attack
Cyber Threat Detection Using Indicators of Attack
Network Monitoring for Anomalous Behavior