Born into a family of the highest social class — nobles, aristocrats, royalty. It describes the birth, not the money or the behaviour: a high-born person is one whose family already had rank before they were born, and you cannot become high-born later by getting rich or famous. It is an old, literary word. You meet it in history books, fantasy novels, period dramas, and translations of old stories — 'a high-born lady', 'his high-born wife'. Almost nobody says it about a living person today in ordinary conversation; modern English would say 'from a very rich family' or 'from an old aristocratic family'. Because it belongs to that old world, it often carries a faint flavour of the speaker's attitude: sometimes admiring, sometimes slightly mocking, as if to say this person expects to be treated well. Its opposite, 'low-born', is much harsher, and that pairing tells you the word comes from a time when people really believed birth decided worth. The spelling 'highborn', without the line, is also correct and quite common.