An index can be understood as a list or reference point that helps you find specific information or things. It is like a map or catalog that organizes and points you to the right direction. Full definition
A funny thing, clients will pay managers to invest their funds in index funds for a fee, when they could simply do this themselves very easily for little to no - fee. (sleepycapital.com)
Most other stock market indexes use a «weighted average market capitalization» system, in which more of the fund's money is invested in larger companies and less in smaller ones. (fool.com)
Human beings may be grouped according to any number of indices of similarity. (religion-online.org)