Consumer Price Index For All Urban Consumers (CPI-U)

What Does Consumer Price Index For All Urban Consumers (CPI-U) Mean?
A measure that examines the changes in the price of a basket of goods and services purchased by urban consumers. The urban consumer population is deemed by many as a better representative measure of the general public because most of the country's population lives in highly populated areas, which represent close to 90% of the total population. 

Investopedia explains Consumer Price Index For All Urban Consumers (CPI-U)
CPI is the most frequently used statistic for identifying inflation or deflation. The CPI-U only considers the prices paid for goods and services by those that live in urban areas. Rising CPI-U figures means that the prices of goods/services within the urban population are becoming more expensive and can be a sign of rising inflation.

All variants of the CPI are similar to cost of living indexes as they assess prices in the market based on the goods and services needed to achieve a given standard of living. Different measures of CPI differ from cost of living indexes because they do not account for changes in other facets of standard of living, such as changes in environmental factors.