Heroku is a platform that allows developers to build, run, and operate applications entirely in the cloud. It provides tools and services to allow developers to focus on building apps rather than managing infrastructure. Key features include automatic deployment from Git, scalability with a single command, add-ons for services like Postgres and monitoring, and collaboration tools for teams. The document provides case studies and discusses core concepts like the deployment workflow, releases, logging, and dynos before inviting the reader to sign up and learn more.