Ruby is an OOP (object-oriented programming) language that was designed to simplify the process in creating a s/w application without losing the power of the more complex programming languages. It allows you to use simple command words, to create powerful applications in a short time and with less code.
Ruby on Rails however is a web application framework, that was written with Ruby programming language. Ruby on Rails simplifies the process in creating application structure. It uses a massive array of pre written libraries to carry out different operations within an application, like form data validation, date and time , application templates, formatting and session management.