This is called linear growth. For example, heapsort and mergesort have this characteristic. . This is called polynomial growth. Computer applications with greater than about 3 are often impractical. They just take too long to run for any reasonably large problem.
Selection sort is an example of a polynomial growth rate algorithm.
This is called exponential growth. In computer science, we traditionally use the constant 2, but the any other positive constant could be used to express the same idea. That is, It may appear strange to use the equals sign between two BigOh expressions. Since BigOh defines a set of functions, the notation means that the set of functions is contained in the the set of functions . Note that it is not true that if then .