In trading, index providers calculate and distribute stock and other asset class indices. One of the important roles of the index provider is to classify and define markets, as their indices represent a market, or a proportion of a market, and provide a benchmark of performance for that market or sector.
The four major index providers are S&P Dow Jones Indices, MSCI, FTSE Russell, and Bloomberg, although there are other smaller providers including Morningstar, CRSP, and Solactive.