Historical military term for a field headquarters or the general staff, especially in pre-modern Japanese contexts. Rare in modern usage; mostly encountered in historical texts or set phrases like 帷幄上奏.
The 帷幄上奏 was a system in which matters concerning military command were reported directly to the Emperor.
You may come across the word 帷幄 in historical novels.
direct appeal to the throne by the military
From Chinese 帷幄 (wéiwò), literally 'curtains and tent', referring to the enclosed space where military commanders planned operations. The Japanese reading いあく is the on'yomi. The term is now largely historical.