SEO Glossary: U
UGC : An acronym for User Generated Content.
uptime : The percentage of time a Web site is up and running, not including scheduled maintenance periods.
URL: An acronym for Uniform Resource Locator.
User-Agent HTTP header : Information describing whether a visitor to a Web site is a person or a search engine robot.
user-agent sniffing : A process that identifies spiders coming to a Web site, enabling the Webmaster to keep out bad spiders.