According to lindyexchange.com, a lindy exchange is "when a city decides that it wants to open up its doors to Lindy Hoppers all over the world. Events are scheduled, performances are set, people offer to host visitors, and general merriment is had by all. It’s an incredible opportunity to visit a new city, dance with new people, build the Lindy Hop community, make new friends, and get little or no sleep! (Or something a lot like that....)" Sounds about right.