The Consumer Price Index (CPI) is a popular measure of inflation that tracks the prices of a basket of goods and services over time. It is used by policymakers, economists, investors, and consumers alike to understand the cost of living and how it changes over time. Synonyms for the CPI include the cost of living index, inflation rate, consumer inflation index, and price index. Each of these terms highlights a different aspect of the CPI, but they all refer to the same basic idea: tracking the prices of goods and services to measure changes in the overall cost of living.