What is Ruby on Rails?

Ruby on Rails is a server-side web application development framework written in Ruby language by David Heinemeier Hansson. It allows you to write less code than other languages and frameworks. It includes everything needed to create database-backed web applications according to MVC pattern.
It is opinionated software. There are two major guiding principles:
Don't Repeat Yourself (DRY): DRY is a principle of software development which states that "Every piece of knowledge must have an authoritative, unambiguous, single representation within a system. If same piece of code will not repeat again and again, code will be more maintainable, extensible and less buggy.
Convention Over Configuration (CoC): It provides different opinions for the best way to do many things in a web application.