A technology by which a webmaster can deliver customized advertising based upon the IP address of the visitor. It allows a site to serve local language or content to specific visitors.
It is the technology used in cloaking, to identify search engine spiders from their IP address and route them to different version of the requested page.
Can be used ethically to route spiders around dynamic webpages which require a database query, to simpler pages that spiders can process, all the while avoiding duplicating content.