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Keyword is a term used in reference to several different types of online content. First, it is a short word or phrase that people search to find content. Second, it is a short word or phrase that is repeated in content — either naturally as one writes, or deliberately with intent to salt the content with the keyword — which is taken as an indication of the focus of the content. Keyword optimization is the aspect of search engine optimization that aims to make a match between material on websites and material that people are searching for by including content with appropriate keywords, and spreading keywords through the content in an appropriate way.
The reason that keyword optimization is important is that it is one of the elements that search engines use in ranking sites and presenting them to users in search results. The better the search engine rankings, the higher the traffic to the site is likely to be. But in order to perform keyword optimization, it is necessary to know what keywords people are searching for.
A keyword database helps site owners and webmasters get information about each keyword’s popularity and value. Some keyword databases are free and some must be purchased or subscribed to. Based on the information in the keyword database and the focus of the website they are working on, the site owners or webmasters may decide to include content using particular keywords. In this case, they may write or spec an article that by its nature would incorporate the keyword in a prominent way. They may also follow or promulgate writing guidelines that aim to ensure sufficient use of the keyword.
To make sure that the number of times a keyword appears is sufficient, it is possible to apply a measure called keyword density. Some experts think that keyword density is a crucial element in search engine optimization. Keyword density is determined by dividing the number of keywords in the content by the total number of words in the content. Other measures that may be used in keyword optimization are keyword prominence, meaning how obvious they are, and keyword proximity, meaning how close together the keywords are.
Keyword optimization is made more complicated, however, because different search engines define keywords in different ways. The way Google™ defines a keyword is different than the way Yahoo!® does, making optimizing for both search engines a bit more difficult. Google™ considers the word or phrase itself and nothing else as the keyword. Yahoo!® counts both inflected forms of the word or phrase, such as plurals, as well as synonyms.