A volume index or quantity index is a numerical time series measure designed to help compare how the production of some class of goods and/or services, taken as a whole, differs between time periods or geographical locations. Compare price index.
As compared to a price index, a volume index takes into account price changes and reflects the level of production without inflation.
Volume or quantity indexes can be constructed by year-to-year chaining just as price indexes can be.
External references: OECD glossary entry