An appearance of Vishnu, worshiped in Venkatachalam.
Tirupati, Venkatachalam, Sheshachalam are the same place.
Venkateshvara, Balaji, Srinivasa are names of Vishnu worshipped there.
The philosopher Ramanuja was meditating on Venkateshvara, when a young (bala) boy came and interrupted his meditation. When he later went to the temple to worship Venkateshvara, he saw that he was the little boy. Since then, Venkateshvara has been called Balaji, where ‚ji‘ is a reverence.