All-around defense "fire guard" or perimeter defensehttps://www.marines.mil/news/publications/Documents/FM%203-21.8%20%20The%20Infantry%20Rifle%20Platoon%20and%20Squad_5.pdf "8-133. A perimeter defense allows the defending force to orient in all directions." is a type of defensive fighting position intended to give military units the ability to repel attacks from any direction.
The positioning of the outer defensive fighting positions of a unit, is circular or triangular,https://www.marines.mil/news/publications/Documents/FM%203-21.8%20%20The%20Infantry%20Rifle%20Platoon%20and%20Squad_5.pdf "The trace of the platoon is circular or triangular rather than linear" from a bird's-eye view.
One version consists of soldiers forming a wide circle around the soldier in charge (and radioman etc.) with a spacing typically of 3–4 metres between each person (on the circle's circumference).
When a group of soldiers relocate as a part of a defensive operation, a perimeter defense can be temporarily maintained without cover.
See also Defensive fighting position Infantry tactics List of military tactics Fortification
References