the four borders of ancient China; (by extension) the whole world; the entire country

(colloquial) loyal to one's friends; straightforward and generous in character

(Traditional Chinese Medicine) a collective term for the four reservoirs of the human body: the sea of marrow (髓海 suǐ​hǎi), the sea of blood (血海 xuè​hǎi), the sea of qi (气海 qì​hǎi), and the sea of water and grain (水谷之海 shuǐ​gǔ​zhī​hǎi)