User Interface (UI) is the aggregate by which users interact with a device, machine, computer program or tool. The UI provides the user with the ability to input data and provides an output to reflect the effects of the users' manipulation.

The two states of a Web document (indexed and relevance to a given set of queries) cannot be determined at the same time. The more queries to which a page is known to be relevant, the less information about the page’s indexing status can be determined. The more information about a page’s indexing status that is known, the fewer queries to which the page is relevant.

The address system used by the Internet to locate resources such as web sites. A Uniform Resource Locator includes the type of resource being accessed (such as gopher or hypertext), the address of the server, and the location of the file. Usually abbreviated as URL.

The number of individuals who visit a website. If one user visits a website 4 times, the statistics will show that 1 user has visited.

The practice by major search engines like Ask, Google, Live, and Yahoo! of melding results from several search databases to provide the user with a more diverse selection of search listings (usually combining video, news, blog, Web, book, and other search tools). Aka Blended Search.

The practice by Universal Search-capable services of augmenting search results with additional, supplemental listings not normally included in the standard 1..10 listings. Universal Search Injection listings usually have more complex structures, provide more information, and are more transient in nature than normal search listings . Universal Search Injections may include links to several documents.

From the SEO side, an update is any noticeable change to the way a search engine behaves. From the search engines’ side, an update is any intended change in a search engine’s makeup or data. Matt Cutts offers an incomplete explanation of a Google update in his December 2006 Explaining Algorithm Updates and Data Refreshes post. He wrote a similar post in September 2005 with What’s An Update?. I don’t expect Matt to confirm every algorithmic change. That would pretty much defeat the purpose of many of them. Yahoo! and Windows Live occasionally issue “weather reports”. Matt has informally issued some on Google’s behalf.

An abbreviation for Uniform Resource Locator.

These are the site listings that appear in Google with nothing more than a URL. Matt Cutts explained that they are uncrawled links that Google knows something about from inbound linkage. Google will (or used to) occasionally pull a description from the Open Directory Project for uncrawled links, but you often see them without any description at all. Uncrawled links are not shown in Google’s SafeSearch mode. Matt also discussed them here.

The measure of how simple it is for a visitor to complete a desired task on a website. Generally, sites with high usability or user-friendliness are more popular and successful than sites that are difficult to use.

An acronym for Unique Selling Point or Proposition. This is a determining factor in what makes a product or service different from the rest.