Price indicators are economic tools used to measure the cost of goods and services. They are used to track changes in the cost of goods and services over time, and can be used to predict future trends in the market. The four-letter tags associated with price indicators are CPI, PPI, GDP, and GNP. CPI stands for Consumer Price Index, which measures the average change in prices paid by consumers for a basket of goods and services. PPI stands for Producer Price Index, which measures the average change in prices received by producers for their goods and services. GDP stands for Gross Domestic Product, which is the total value of all goods and services produced within a country's borders. Finally, GNP stands for Gross National Product, which is the total value of all goods and services produced by a country's citizens, regardless of where they are located.