What term refers to network elements that are isolated to protect them from external attacks?

The term that refers to network elements that are isolated to protect them from external attacks is a Demilitarized Zone (DMZ). A DMZ is a physical or logical subnetwork that contains and exposes an organization's external-facing services to an untrusted network, typically the internet. In this setup, the DMZ serves as a buffer zone between an internal secure network and external networks, ensuring that external entities can access certain services without gaining direct access to the internal network.

This architecture not only helps to mitigate potential attacks by segregating server resources from sensitive internal data but also allows for additional security measures to be implemented, such as firewalls and intrusion detection systems, which monitor and control traffic between the DMZ and both the internal network and the internet.

In contrast, the other terms listed represent different concepts in network security and data management. Database Activity Monitoring focuses on tracking and analyzing database activity to detect suspicious behavior. Defense in depth is a layered security approach that uses multiple security controls to protect information assets rather than relying on a single security measure. Data mining involves analyzing data sets to discover patterns and relationships within the data, rather than focusing on network isolation.