What are keywords?
Keywords or key phrases are the search terms that a user types into a search engine text box in order to find information relevant to their search. For example if you search Google for |chess| you will see something like this:
This is called the Search Engine Result Page or SERP and Google tries to put the most relevant result first, then the next and so on. What you see is the top ten results out of, (in this case) over 24 million pages ranked in order of relevance.
Google can’t know if the user is looking for something more specific like for example; chess sets, chess clubs or the rules of chess, so the results will be a broad range of pages related to chess in some way.
A user seeking a chess club in Chicago is more likely to search for |chess club chicago| in which case they would see something like this:
Notice how for this more specific search the number of candidate pages has gone down from over 24 million to around 1.8 million. As Google says “Choosing the right search terms is the key to finding the information you need”.
The obvious corollary for site owners is that choosing the right keywords to optimize for is the key to maximising the number of visitors and conversions (the percentage of visitors who take a desired action like buy a product or subscribe to a newsletter). In general the higher you are in the SERPs the more visitors you will have and the more specific the keywords the higher the conversion.
Users search in different ways with different words and site owners need to know what these keywords and phrases are for their particular business.