onsen

This term refers specifically to the Japanese cultural practice of bathing in naturally heated mineral water. While it can describe the geological hot spring itself, it most commonly refers to the facility or bathhouse where people bathe. It carries a strong connotation of relaxation, purification, and social bonding within a traditional Japanese setting.

In English usage, the word is treated as a standard countable noun. Because it is a loanword from Japanese, it follows English pluralization rules in most contexts, though some writers may retain the Japanese singular form for the plural.