Let us begin with a most familiar scenario in online shopping. We are searching for Macbook Air on Amazon.com. When we scroll down the product page in the end we get to see similar products like Macbook, Macbook Pro and other Apple related accessories and items. How did Amazon.com suggest you to look in for similar products in the same category just like a salesman puts you before similar products when you go to a real store? This is the power of Machine Learning applications in this case it is a recommender system which plays a massive role in increasing the sales of a e-commerce websites. What is the working fuel behind these recommender systems?