What term describes an entry into or out of a security perimeter?

The term that best describes an entry into or out of a security perimeter is "security portal." A security portal typically refers to a designated point that is specifically designed and equipped to control access into a secured area. This can include various security measures such as access control systems, surveillance, and identification verification procedures.

In a security context, portals are fundamental as they serve as the controlled gateways through which individuals must pass, making them integral to maintaining the integrity of the security perimeter. Portals are designed not only to facilitate entry and exit but also to enhance security by managing who is allowed to enter and exit the area.

Access points, while also denoting entry or exit locations, might not always carry the same implication of security measures being in place as a security portal does. Security checkpoints involve screening processes but are often specific to locations rather than general access points. Restricted entrances suggest limited access but do not inherently imply controlled, monitored entry or exit like a security portal.