According to Wikipedia,

Combinatorics is an area of mathematics primarily concerned with counting, both as a means and an end in obtaining results, and certain properties of finite structures. It is closely related to many other areas of mathematics and has many applications ranging from logic to statistical physics, from evolutionary biology to computer science, etc.

In this blog, we’ll primarily use combinatorics for counting, with a big focus on binomial and multinomial coefficients, because that’s what I find most interesting; I’ve only taken one combinatorics class, so I’m not an expert, but hopefully everything in this blog will be insightful regardless.