Prices and price level
Prices are of great importance in macroeconomics as indeed they are in microeconomics. However, in microeconomics we are more interested in prices of individual goods and services and such prices are rarely important for the economy as a whole although there are exceptions (for example, the price of oil).
In macroeconomics we are more interested in how prices change on average . We define the price level as a weighted average of several different prices. If p 1 is the price of gasoline and p 2 the price of oil, then 10 p 1 + p 2 is a price level. It is a weighted average of two prices with weights 10 and 1. Normally, the price level is defined using many more prices.