What is the meaning of broken in?

verb

• Enter someone's (virtual or real) property in an unauthorized manner, usually with the intent to steal or commit a violent act.
  • usage: "Someone broke in while I was on vacation"; "They broke into my car and stole my radio"; "who broke into my account last night"
  • synonyms: break in, break
• Break into a conversation.
  • usage: "her husband always chimes in, even when he is not involved in the conversation"
  • synonyms: chime in, cut in, put in, butt in, chisel in, barge in, break in
• Start in a certain activity, enterprise, or role.
  • synonyms: break in
• Intrude on uninvited.
  • usage: "The nosy couple broke in on our conversation"
  • synonyms: break in
• Break so as to fall inward.
  • usage: "He broke in the door"
  • synonyms: break in
• Make submissive, obedient, or useful.
  • usage: "The horse was tough to break"; "I broke in the new intern"
  • synonyms: break in, break

adjective

• Tamed or trained to obey.
  • usage: "a horse broken to the saddle"; "this old nag is well broken in"
  • synonyms: broken