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.
—related noun check-in
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.
—related noun check-in
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005