Wordtracker is a popular keyword research tool designed to assist search marketing professionals and webmasters in identifying important keywords and phrases relevant to their site. It provides detailed information on the number of searches, predicted number of daily searches, competing pages and KEI data.

Xenu is a most popular Internet based program used for checking the validity of links.

Xenu link sleuth is a free software program that checks broken links both internally and externally. The software also aids in the creation of sitemaps.

XHTML or Extensible Hypertext Markup Language is a set of specifications that were created in order to move HTML to XML.

XML or Extensible Markup Language is a scripting language that allows the programmer to define the properties of a document. It is often used in web based applications as it is easy to use.

Yahoo is one of the most popular web based directory.

Yahoo! Answers is a Yahoo! owned free Q&A site that allows people to both ask and answer questions which then results to free content.

Yahoo Directory is on of the oldest and most trusted directories.

Yahoo! Search Marketing is a paid search platform and owned by Yahoo! It was once called Overture

Yahoo Site Explorer is a research tool which webmasters can use to see what pages Yahoo! has indexed from a website, and what pages link at those pages.

YouTube is a video site owned by Google wherein members can upload their own videos for other people to watch.

Zone is another term for the shortening of a topic within a search engine to allow the user to be given results within defined parameter - such as date range or location