The Collaborative International Dictionary of English v.0.48:

check-in \check"-in\ (ch[e^]k"[i^]n), n.
   The act of registering as a guest at a hotel, inn, motel.
   etc; the act of checking in. Used also attributively, as the
   check-in counter at a hotel.
   [PJC]

WordNet (r) 3.0 (2006):

check-in
    n 1: the act of reporting your presence (as at an airport or a
         hotel)