check in phrasal verb definition in Plane travel topic from the Oxford Advanced Learner's Dictionary

check in

 phrasal verb: Plane travel topic
to go to a desk in a hotel, an airport, etc. and tell an official there that you have arrived Please check in at least an hour before departure. We've checked in at the hotel. to leave bags or cases with an official to be put on a plane or train We checked in our luggage and went through to the departure lounge.