How do we buy things in our day-to-day lives? We ask our friends, research the product specifications, compare the product with similar products on the Internet, read the feedback from anonymous users, and then we make decisions. How would it be if there is some mechanism that does all these tasks automatically and recommends the products best suited for you efficiently? A recommender system or recommendation engine is the answer to this question.
In this introductory chapter, we will define a recommender system in terms of the following aspects: