Ruby on Rails is a web application framework built on Ruby. It was created by David Hansson in 2004 and follows conventions like MVC architecture and RESTful design. Rails makes it easier for developers to build database-backed web applications by providing default structures for common tasks and promoting practices like DRY (Don't Repeat Yourself) and agile development. The framework includes everything needed to build a full-stack web app with models, views, controllers, mailers and support for databases through ActiveRecord.