Definitions
1.verbTo announce or record one's own arrival at a hotel, airport etc."We got to the hotel last night and checked in at the front desk."
2.verbTo verify a person's information and record their arrival, such as at a hotel, airport, etc."The clerk checked us in at the front desk."
3.verbTo contact another person in order to keep the other person informed of one's situation."Kelly has to check in with her parole officer today."
4.verbTo return (a book to a library, source code to a repository, etc.).
5.verbTo visit in order to see how someone is doing."I just wanted to check in after your accident. How are you recovering?"
6.verbTo enter solitary confinement at one's own request for protection from other prisoners.