Infinity is very mysterious. It defies our common sense. Yet, it plays a very significant role in Calculus, particularly, differentiation and integration, which have a lot of real-life applications. To name a few, operation research and data science, where gradient descent and back-propagation in neural networks apply differentiation and Chain rule to achieve the desired outcomes. So, to understand Calculus better, it is natural that one would try to understand what infinity is.