In Algebra, we learn about functions of various types. These functions are often seen in a progression from least complicated (linear) to most complicated (piecewise with nonlinear parts). And then there are other types of functions in-between: exponential, quadratic, polynomial, radical, and logarithmic. But with all their differences and unique properties, these share a common trait of being functions that we can graph in a coordinate plane.

What are some other things you can observe to have that same quality of functions: unique, but sharing a common trait or purpose?