海内 is a classical Chinese term meaning 'within the seas' — it refers to the whole country (China) or the world, often used in formal or literary contexts. You'll encounter it in idioms like 海内存知己 ('a bosom friend afar brings a distant land near') and in historical or poetic writing. It's a place word (p.w.) that functions like a noun or adverb, typically appearing as a subject or modifier.