Ruby on Rails
Rails is a software library that extends the Ruby programming language. It is software code that is added to the Ruby programming language. Technically, it is a package library (specifically, a RubyGem), that is installed using the operating system command-line interface.
Rails is a framework for building websites. As such, Rails establishes conventions for easier collaboration and maintenance. These conventions are codified as the Rails API (the application programming interface, or directives that control the code). The Rails API is documented online and described in books, articles, and blog posts. Learning Rails means learning how to use the Rails conventions and its API.