Stock photography according to wikipedia - “Stock photography consists of existing photographs that can be licensed for specific uses. Book publishers, specialty publishers, magazines, advertising agencies, filmmakers, web designers, graphic artists, interior decor firms, corporate creative groups, and others use stock photography to fulfill the needs of their creative assignments.
A customer who uses stock photography [...]

Here is a list I have compiled of stock/microstock photography resources and articles to help you start selling your images online.
Stock/Microstock Photography Information
Microstock Diaries - Great site! Ins and outs of the stock photography market
Microstock Forums - discuss and promote your stock photography
Microstocks Curse or Blessing? - Extensive article on selling your photos through [...]