Floridaâs tract of coral reefs has the honor of being the third-largest barrier reef ecosystem in the world. However, it could soon be a thing of the past, as the acidification of the oceanâs water is dissolving it faster than it can rebuild.
index (plural indexes or indices) 1  An alphabetical listing of items and their location. The index of a book lists words or expressions and the pages of the book upon which they are to be found. 2  The index finger; the forefinger. 3  A movable finger on a gauge, scale, etc.
In most cases, an index is used to quickly locate the data record(s) from which the required data is read. In other words, the index is only used to locate data records in the table and not to return data. A covering index is a special case where the index itself contains the required data field(s) and can answer the required data.