Final answer:
A directive sent through the Defense Messaging System is called a policy directive, which is a formal instruction that guides actions within the military or government.
Step-by-step explanation:
A directive transmitted via the Defense Messaging System (DMS) is known as a policy directive. The DMS is a secure messaging service used by the United States Department of Defense and other authorized agencies to send official communications. A policy directive is generally a formal instruction from a high-level organization within the military or government that guides actions in a specific way to achieve intended outcomes.
In summary, within the Defense Messaging System, a Policy Directive represents an authoritative communication conveying policies or instructions, and its transmission through DMS ensures the secure and reliable delivery of these directives to the designated recipients in the defense community.