SNMP - Engine ID
The Engine ID is a feature specific to SNMPv3, and was introduced as part of its enhanced security model. The engine ID uniquely identifies each SNMPv3 entity, be it an SNMP agent or an SNMP manager. The uniqueness of the ID is crucial for security purposes, keeping in mind that SNMPv3 has added security features compared to its predecessors.
The Engine ID is used in the generation of security parameters, and it helps to ensure that the communication is indeed with the correct device. Without unique Engine IDs, there could be potential for security breaches or miscommunication.
Links:
https://forum.networklessons.com/t/how-to-configure-snmpv3-on-cisco-ios-router/1033/66?u=lagapides