Source: Image of Big Mac, Public Domain: http://en.wikipedia.org/wiki/File:McD-Big-Mac.jpg CPI Graph, Creative Commons: http://en.wikipedia.org/w/index.php?title=File:US_Consumer_Price_Index_Graph.svg&page=1
A way to measure the relative change in a value, usually the price of a good or service, over time. If the index number is over 100, that means the price has increased. If the price has decreased, then the index number will be less than 100.
An arbitrarily chosen starting value for an index. It is assigned an index number of 100.
An index published by the US Bureau of Labor Statistics that shows the change in the price of many different goods or services in the United States. It provides a measure of purchasing power.
A relative increase in the price of a good or service over time. A person will need to pay more to receive the same good or service than they did at a previous point in time.