URL

Used interchangeably with web address. Acronym stands for Uniform Resource Locator. URLs can specify the location of a web page, an email address, or a file on an FTP server, among other things.

URL Rewrite

A technique used to help make URLs more unique and descriptive to help facilitate better sitewide indexing by major search engines.

Unique Visitors

A count of individual users who have accessed your web site. It should be noted that the "user session" metric does not yield an accurate unique visitor count, as multiple user sessions can be generated by one unique visitor.

User Session

An instance of an Internet user accessing your web site for a length of time, then leaving. During a user session any number of pages may be accessed. A user session is considered finished once an arbitrarily chosen period of inactivity - typically 30 minutes - is exceeded.

Unethical SEO

The opposite to Ethical SEO. It involves employing underhand or illegal activities to increase search engine ranking. They are many unethical seo practices including cloaking, gateway pages, keyword spamming.

Usability

How easy it is for customers to perform the desired actions.

Usage Data

Things like a large stream of traffic, repeat visitors, multiple page views per visitor, a high clickthrough rate, or a high level of brand related search queries may be seen by some search engines as a sign of quality.

Usenet

A search service which is focused on a particular field, a particular type of information, or a particular information format.

USPTO

Acronym for United States Patent & Trademark Office.

User Agent

This is the identity of a web site visitor, spider, browser, etc. The most common user agents are Mozilla and Internet Explorer.

Update

Search engines frequently update their algorithms and data sets to help keep their search results fresh and make their relevancy algorithms hard to update. Most major search engines are continuously updating both their relevancy algorithms and search index.