A pen or enclosure for pigs. The farmer built a new sty to house the growing number of pigs on his farm.
His room was such a sty that you could barely see the floor under all the clothes and books.
An inflamed swelling on the edge of an eyelid, caused by bacterial infection of the gland at the base of an eyelash. She had to visit the doctor because the sty on her eyelid was becoming increasingly painful.