Highborne were a sect of Kaldorei. They are Night Elves.
For generations, the night elves had experimented with the Well of Eternity. As they mastered its energies and unraveled the mysteries of the arcane, they became gifted and ambitious sorcerers. The greatest of these magic users were Queen Azshara and a sect of night elven society known as the Highborne. Thewir unbridled pursuit of magic led to wondrous accomplishments, but it also brought their empire to ruin.