Ruby is an interpreted, object-oriented programming language that centers around simplicity and ease of use. In it’s most basic form, it can be used to create console applications, manipulate files and do many other things.

Rails, on the other hand, is a web framework built to enhance the Ruby programming language. With it, you can quickly build websites by using Ruby, but with some added features. It is a technology used by sites like Twitter, Groupon, Indiegogo, Airbnb, Souncloud, and more.

http://railsapps.github.io/what-is-ruby-rails.html