There is a meta tag for keywords that was created in the early days of search engines. They were used by a search engine called Alta Vista. Google has never used the keyword tag; It is virtually worthless. Search Engine spam started in the days of the keyword meta tag and have sealed its fate; The tag is dead. No search engine in their right mind will begin using it.
SEO is more about the arrangement of content on a site and marketing that content to search engines than it is about keywords. The keywords need to be considered for SEO as far as what people will search for in the search engines – then those words need to be included in the content. What the search engines look at is what people can see not information that they can not. It is about putting the words in links, headlines, text and titles.