A statistical measure of the
value of a certain
portfolio of
securities. The portfolio may be for a certain class of security, a certain
industry, or may include the most important securities in a given
market, among other options. The value of an index increases when the aggregate value of the underlying securities increases, and decreases when the aggregate value decreases. An index may track
stocks,
bonds,
mutual funds, and any other security or
investment vehicle, including other indices. An index's value may be
weighted; for example, securities with higher
prices or greater
market capitalization may affect the index's value more than others. One of the most prominent examples of an index is the
Dow Jones Industrial Average, which is weighted for price and tracks 30 stocks important in American markets.