Once a week, for an hour or two, the host venue provides a space in their pub/café/tea room/hotel lounge for people to sit and chat, and provides free tea, coffee and some sort of nibbles for the visitors to enjoy during the session.
Some venues offer a packet or two of biscuits, some provide cakes, sandwiches or sausage rolls, but all offer tea and coffee. Some MeetUpMondays visitors even bring their own baking to share, to help fuel the chat and to support the venue!