The h-index was developed by J.E. Hirsch and published in PNAS 102 (46): 16569-16572 November 15 2005.
The h-index is based on a list of publications ranked in descending order by the Times Cited. The value of h is equal to the number of papers (N) in the list that have N or more citations.
This metric is useful because it discounts the disproportionate weight of highly cited papers or papers that have not yet been cited.