Keyword is a word in the text that gives a concise description of the content of a text document, which allows user to better identify its subject matter.
Keywords in the Web are used mainly for searching and are the main way to organize content.
Key words in text analysis, (including when building an index in search engines), are especially important and representative of a particular nature of words in a text, the set of which can give a high-level description of its content for the reader. Key words (KW) are characterized by the following traits:
In HTML, to specify keywords, there are meta elements with the respective keywords. This way of specifying keywords opens up even more opportunities for abuse. As a result, only some search engines use this metatag as a factor to improve the ranking of the pages, while others don’t. Historically, this aspect was overused in SEO and is now ignored by the leading search engines, like Google.
For example, Google often ignores the keywords in the tag, because of too much abuse in the past. However, they are used by other user agents (for example, web browsers for searching bookmarks).
In XHTML microformats, the keywords describing the document are presented as a list of links, each of which should lead to a page containing a list of documents that also has this keyword. Thus, the possibility of abuse is somewhat reduced, since each link should lead to real content. For such keywords, the term "tags" are more often used, and at the code level they are implemented using the micro-format tag-rel.