weighted mean

What is a weighted mean? When should it be used instead of a simple mean?

need to reference. We have just one reference that is Statistical Techniques in Business & Economics with Student CD, by Douglas A. Lind, William G. Marchal, and Samuel A. Wathen, 15th Edition, MCGraw-Hill/Irwin, 2012. ISBN-13 9780073401805.
in chapter 3: Describing Data: Numerical Measures