A concierge is a resident caretaker of a block of flats, apartments, or of a small hotel.
In a large hotel the concierge takes care of the wants and needs of guests, booking tours, making restaurant and theatre reservations, and so on. It's a very broad job description, and is highly important work.
Concierges at the best hotels are proud of their ability to provide guests with whatever they need within the bounds of possibility.