A price index adjusted for changes in factors such as the quality of goods using a hedonic pricing model. This allows inflation to be measured more accurately.
Many indices use hedonic adjustments on some components (e.g. prices of the products of fast changing technology), other quality adjustments on other components, and no adjustment at all to components that are not deemed to require it.
Adjustments for quality are made to a number of widely used indices including the UK's CPI, its equivalent in other EU countries, and the US CPI.