A keyword is a word that is extremely relevant to the content it is associated with. Imagine a video on a popular video streaming site. It is about motor cars. Two keywords associated with the video might be ‘motor’ and ‘cars’ but also the name of the driver say ‘Hill’. In an article the keywords might not always be so obvious but usually they will be written regularly throughout the article. A discussion of Hill’s big win in the motor race might mention the race, Hill and motor cars regularly and the keywords (most important words) would be things like ‘Hill’, ‘cars’, ‘motor’ and ‘race’.
Keywords are useful to users as they can assist in ways such as suggesting other articles that are similar automatically using a sidebar that displays other articles with the same keyword. Users are often given the opportunity to click the keywords at the end of an article to search using that keyword and find other related content. Keywords are also important for search engines as they help understand the core messages of content. Note that search engines often use their own algorithmic methods to determine keywords rather than relying on those suggested by webmasters.