The arithmetic mean is the average:

Population mean and sample mean are examples of arithmetic means.
The geometric mean is used to find a compound growth rate:

The weighted mean weights each value according to its influence:

Calculate and interpret measures of central tendency.
The harmonic mean can be used to find an average purchase price, such as dollars per share for equal periodic investments:

The median is the midpoint of a data set when the data are arranged from largest to smallest.
The mode of a data set is the value that occurs most frequently.