A Google Custom Search Engine enables Web site authors to host a Web site (or Web) search box and search results on on their site. Users can customize the search engine that is built using Google’s core search technology. In creating your own Google Custom Search Engine you can prioritize or restrict search results based on specific Web sites and pages you specify. Once you’ve defined your search engine, Google provides code for a search box that users can copy and then paste right in to their own Web site or blog.
See also “Google Products and Services” in the Quick Reference section of Webopedia.