Ruby on Rails, often referred to as Rails, is a popular open-source web application framework written in the Ruby programming language. Created by David Heinemeier Hansson in 2004, Rails is designed to make web development faster and easier by providing developers with a structured environment and a rich set of tools and libraries. Rails follows the Model-View-Controller (MVC) architecture, which helps organize application logic and separate concerns, making it easier to build and maintain web applications. One of Rails' key principles is "Convention over Configuration," meaning it comes with sensible defaults that reduce the need for configuration, allowing developers to focus on writing code that delivers value.

Rails is particularly known for its developer-friendly features, such as scaffolding, which automatically generates basic CRUD (Create, Read, Update, Delete) interfaces, and its emphasis on test-driven development (TDD), encouraging developers to write tests alongside their code. Rails has been used to build many well-known applications, including GitHub, Shopify, and Basecamp, making it a proven choice for startups and enterprises alike. The framework's focus on simplicity, productivity, and developer happiness has contributed to its enduring popularity in the web development community.