The ________ is a semi-trusted network zone that separates the untrusted internet from the company's trusted internal network.

The term "DMZ" or "demilitarized zone" refers to a network architecture designed to enhance security by creating a separate area that acts as a buffer between an untrusted external network, such as the internet, and a trusted internal network. The DMZ typically hosts public-facing services, such as web servers or email servers, allowing external users to access these services while providing a protective barrier for the internal network. This design minimizes the risk of unauthorized access to sensitive internal resources, as any potential attack or breach occurs within the DMZ rather than the core internal systems.

In contrast, the other options do not represent a widely recognized network security architectural concept. A buffer zone, while it might sound relevant, is not a standard term used in the context of network segmentation in cybersecurity. CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) is a security measure used to verify user authenticity rather than a network structure. Similarly, a hidden field zone does not have any established significance in network security or segmentation. Thus, the DMZ stands out as the correct choice due to its specific role in network security management.