A weight in statistical terms is defined as a coefficient assigned to a number in a computation, for example when determining an average, to make the number's effect on the computation reflect its importance.
An illustration of 'weight' and 'weighting' is the calculation of the harmonised index of consumer prices (HICP) performed by Eurostat. The HICP is composed of prices for a 'basket' of items regularly purchased by consumers. However, some items such as food and newspapers are purchased more frequently than others, such as car insurance or a television set. To account for this, the various items in the basket are assigned a weight to reflect the total consumer expenditure on these items even though they may be low-cost individual purchases.