What is defined as a line beyond which surface-to-surface fires may fire without additional coordination?

The term defined as a line beyond which surface-to-surface fires may fire without additional coordination is the Coordinated Fire Line. This line establishes a boundary that allows units to engage targets beyond it without needing further permission for each engagement, facilitating timely and coordinated fire support.

The reason this concept is important in the context of fire support is that it helps streamline operations and communication on the battlefield, allowing for a more rapid response to threats. The use of a Coordinated Fire Line maximizes the efficiency of fire support while ensuring that friendly forces are not inadvertently targeted.

In contrast, other options such as the Fire Support Coordination Line or Restrictive Fire Line might denote different parameters for coordinating fire, introducing additional requirements for communication or engagement. A boundary typically refers to the delineation of areas between units but does not inherently convey the conditions for fire engagement like the Coordinated Fire Line does.