Ruby on Rails is an open-source web application framework written in the Ruby programming language. It is designed to make programming web applications easier by making assumptions about what every developer needs to get started. Rails provides structures for databases, web services, and web pages, as well as a set of libraries and tools that allow developers to quickly create web applications with minimal effort. Rails is a model-view-controller (MVC) framework, which provides a structure for organizing code into logical components. It also provides libraries for accessing databases, rendering HTML and XML, and creating web services.