"Consumer prices index": (CPI). 1. The Consumer Prices Index is a leading measure of inflation in the UK, calculated as the change from month to month in the prices of a standard basket of consumer goods and services. The CPI has replaced the Retail Prices Index (RPI) for a number of purposes as the primary measure of inflation in the UK. Previously known as the Harmonised Index of Consumer Prices (HICP). 2. The Consumer Price Index is one of the leading inflation indices used in the US. Its uses include the limited indexation of certain US pensions. 3. More generally, a consumer prices index is a statistical estimate constructed using the prices of a defined sample of representative consumer items, such as goods and services, whose prices are collected periodically. The index is compared to a base period to give an estimate of periodic inflation rates.