What is Ruby on Rails?

Ruby on Rails, or just Rails, is a web framework written in Ruby. There are plenty of web frameworks available but few if any are as full featured and easy to use as Ruby on Rails. That may sound like an oversimplification but those are two main reasons that web programmers are excited about using Rails.
Most frameworks have to balance features and ease of use and for any decent sized web application they require you to spend large amounts of time configuring all of the reusable parts. This is where Rails excels. Instead of you making the same configuration changes in all of your applications, Rails uses coding conventions to wire the pieces together. By following a few simple conventions when creating your programs, you can take advantage of built-in functionality that you would otherwise had to write code to handle.