TileMill is a tool that allows users to create map tiles for faster loading maps. It uses technologies like Mapnik, Node.js, and Backbone.js to style data and generate map tiles. The document provides examples of how to style map features in TileMill using CSS-like selectors and properties to configure things like line colors and widths. It also mentions technologies that can be used to serve, interact with, and display map tiles generated with TileMill.