A keyword in an Internet search is one of the words used to find matching web pages. It was popularized during the early days of search engine development, as it was not possible to ask natural language questions and find the desired sites. Searches gave the best results if only a few keywords were chosen and searched for. These "keywords" captured the essence of the topic in question and were likely to be present on all sites listed by the search engine.
Keywords are still used today. Many modern search engines have methods for determining which words in a search string are important and are ought to be treated as keywords. Common words like articles (a, an, the) and conjunctions (and, or, but) are not treated as keywords because it is inefficient to do so. Almost every English-language site on the Internet has the article "the", and so it makes no sense to search for it.
Meta elements provide information about a given webpage, most often to help search engines categorize them correctly, and are inserted into the HTML code in the format illustrated above, but are not visible to a user looking at the site.
They have been the focus of a field of marketing research known as search engine optimization (SEO), where different methods are explored to provide a user's site with a higher ranking on search engines. In the mid to late 1990s, search engines were reliant on meta data to correctly classify a web page and webmasters quickly learned the commercial significance of having the right meta element, as it frequently led to a high ranking in the search engines - and thus, high traffic to the web site.
Some search engines such as Google will display the text specified in the content of the META description tag for a page in their result listings. This allows the webpage author to give a more meaningful description for listings than might be displayed if the search engine was to automatically create its own description based on the page content.