What defines a tactical mission task aimed at denying enemy access to an area?

The tactical mission task aimed at denying enemy access to an area is defined as "Block." This task involves positioning forces to prevent an enemy from moving into a specified area or to restrict their freedom of movement. By blocking an advance, friendly forces can control key terrain and protect vital assets while also potentially setting the stage for future operations.

Blocking is a critical task in military strategy; it is essentially the act of creating a barrier to enemy access or maneuvers, which can significantly influence the flow of battle. This mission is often employed in defensive operations, where the primary objective is to safeguard a location or resource against enemy forces. Forces assigned to this task may conduct reconnaissance to identify the enemy's movements and leverage terrain advantages to establish a strong defensive position.

The other options presented describe different types of mission tasks that do not specifically focus on denying access. For instance, a breach is tasked with overcoming an obstacle or enemy position, and a guard involves protecting friendly forces while continuing to conduct operations. Cover typically refers to providing protection from enemy observation or fire, rather than directly denying access to an area.