ordinary cap; field cap; garrison cap
A simple, often military-style cap without a brim or with a soft visor; used in casual or field settings. The term is somewhat dated and may be encountered in historical or military contexts.
兵士たちは略帽をかぶって訓練に参加した。
The soldiers participated in training wearing their field caps.
From 略 (りゃく, 'abbreviated' or 'simplified') and 帽 (ぼう, 'cap'), referring to a simplified military cap.