Ruby on Rails, or Rails for short, is a web application framework that was created in 2004 by David Heinemeier Hansson. Rails is based on Ruby and follows the Model-View-Controller (MVC) pattern, which separates the data, logic, and presentation layers of an application. Rails also follows the convention over configuration (CoC) and don't repeat yourself (DRY) principles, which reduce the amount of code and configuration needed to build a web application. Rails provides many features and tools, such as scaffolding, routing, migrations, validations, testing, and security, that make web development faster and easier.