Meteor is a full-stack JavaScript framework that allows developers to build web applications quickly using a single programming language. It includes a development environment to build the app, a database (MongoDB), and communication protocols (DDP) to connect the client and server. The document demonstrates a simple Todo app built with Meteor that allows users to create, update, and mark tasks as complete. Templates are used to display tasks and counts, while events and helpers interact with the Tasks collection in MongoDB to add, update, and filter data.