What does the word stud mean?

Usage examples for stud

  1. Then, before he pressed the stud, he looked at Cardon curiously. – Null-ABC by Henry Beam Piper and John Joseph McGuire
  2. Ralph the heir had bought some of his uncle's horses, and had commenced hunting with the hounds around him; though he had not as yet withdrawn his stud from the Moonbeam. – Ralph the Heir by Anthony Trollope