By definition, a keyword is an informative word used in an information retrieval system to indicate the content of a document with the expectation of a matching search result.
Keyword research for individual web projects are enormously facilitated by useful tools. Moreover, keyword tools assist greatly in content optimization. Many of these tools are free.
From the standpoint of technical search engine optimization (SEO), a keyword is an important element of a webpage. The relevance of a document is determined by a search engine using a keyword analyzer and checking whether that page matches a search query. Moreover, keyword proximity is a decisive factor.
It is beneficial to accommodate search phrases in the title tag, meta description, header tag and context to set a keyword focus. If this is not the case, it may happen that the search engine does not consider the webpage relevant for a specific keyword search and therefore positions it lower in the ranking or does not list it at all in the SERP. Currently, keywords are not case sensitive since Google interprets all searches based on lower case. In the future, however, Google could introduce a case sensitive search and case sensitivity of keywords would become important.
Too frequent use of relevant keywords on a page (keyword stuffing) may even result in an exclusion from the search engine index. A ranking downgrade is also not excluded.
Recommended is the sensible use of important keywords within a page. An HTML document should ideally be oriented around a single keyword. By means of a good keyword analysis for one’s own industry or business sector you can find out in advance about the relevant keywords for your website.
Both internal and external linking are largely dependent on the context in which and with which link text hyperlinks are linked. Relevant keywords should therefore be present in both cases, so that the linked site can be associated with a concept.
Caution is advised, however. Since the Panda update, Google is more closely observing the external anchor text of a page. If a link text is too frequently used, it may result in penalties for the page (or an entire domain). If a keyword is used in the wrong context or is classified by Google as irrelevant (bad keyword), devaluation may ensue. Many variations being used in link text and value being placed on naturalness can benefit the ranking of a page.
The advertising program called Google AdWords puts special focus on keyword advertising. In search advertising, keyword-based advertising campaigns are crucial. Multiple campaigns and ad groups are created with specific keywords. If one of the keywords is searched, the ad will appear in the search results depending on the bid. In Google AdWords and the search engine optimization, it is particularly advisable to place particular emphasis on the search volume of a keyword, since it may be able to provide an assessment of the potential visitor volume that searches for a particular keyword at Google. Search volume can be determined quickly with the Keyword Tool.
With the introduction of the social network Google Plus, more and more websites visitors surf the web while being logged in with a Google account. For some time now, the keywords a visitor used to get to a website is no longer provided in the reports. Google obscures the personal data and it is no longer available for the general public. If the number of logged-in visitors continues to grow, it may become difficult for webmasters to optimize their sites on a keyword basis. Today the percentage of users that are logged-in when using Google is relatively low, but on a rising trend.
The most searched keywords of the year are listed in Google Zeitgeist and a website operator or SEO may be able to detect future trends with it.