What's "check in" mean? I only heard of it in hotels.

Native speaker’s answer
Rebecca
In this context, "check in" means to talk with someone in order to find out new information. In hotels, "check in" means to report your arrival at a hotel in order to get the service you paid for. Ex: I have to go to a meeting now, but I'll check in with you later. Ex: I have to check that in with my assistant.