Indices are collections of securities that represent the aggregated performance of entire market segments or stock markets. For example, the FTSE 100 (often referred to as the UK 100) tracks the performance of the 100 largest companies traded on the London Stock Exchange. Similarly, the DAX (often referred to as the Germany 30) tracks the value of 30 of the largest German companies traded on the Frankfurt Stock Exchange. Indices are a vital indicator of the economic health of a country, or certain sectors of its economy.