海军 (hǎi jūn) literally means 'sea army' — combining 海 (hǎi), meaning 'sea' or 'ocean', and 军 (jūn), meaning 'army' or 'military force'. It refers specifically to a nation's naval branch, responsible for maritime defense, operations at sea, and protecting coastal and overseas interests. Unlike general military terms, 海军 always denotes an official, organized naval force — not private ships, coast guard units, or fishing fleets.

This word is formal and institutional, used in news reports, government documents, historical texts, and military contexts. It’s commonly paired with country names (e.g., 中国海军, the People’s Liberation Army Navy) or verbs like 建立 (to establish), 部署 (to deploy), or 派遣 (to dispatch). While it shares the character 军 with other military terms like 陆军 (lù jūn, army) and 空军 (kōng jūn, air force), 海军 is distinct in scope and function — exclusively maritime.