A graph is a visual representation of data which facilitates interpretation. However, it is difficult to convey a visual graph to someone else verbally. It is also difficult to make precise statistical inferences from graphs e.g. how do you measure the difference between two graphs?
Numerical measures can be used to solve these problems. They are a set of numbers that convey the meaning of the graph. Numerical measures of a population are called parameters and numerical measure of a sample are called statistics.
Numerical measures can be used to measure the center, variance from the center, and relative standing of a subset of the distribution. Measures of center find the center of the data. The variance shows how data deviates from or varies with respect to the center. Relative standing shows how different sections of the data set relate to one another.