Pareto Chart:
A Pareto chart, also called a Pareto distribution diagram, is a vertical bar graph in which values are plotted in decreasing order of relative frequency from left to right.

Rouse, Margaret. (2011, March). Pareto Chart (Pareto Distribution Diagram). Retrieved from the Whatis.com website:
http://whatis.techtarget.com/definition/Pareto-chart-Pareto-distribution-diagram


Basically, a Pareto Chart displays data in decreasing frequency from left to right.


A clear example can be found in this chart:
http://cdn.ttgtmedia.com/ITKE/uploads/blogs.dir/67/files/2009/02/pareto_chart_customer-complaints.jpg