To help Search Engines to index content of the website, the editor can insert for each category and for each article some specific keywords called meta TAG.
Meta TAGs assign more meaning to the content of a page, or to a group of pages, resuming the subject matter in few words (keywords).
Each keyword rapresent for a search engine a suggestion to offer that specific page when somebody try to search just that word.
For example in a webpage an editor inserts the recipe for the apple pie. In the body text he writes a lot of information regarding the ingredients and the process to follow to make the pie, but probably the words apple and pie could not be written more than one times, just in the title of the page. Because of this, a typical search engine process could not well identify and then associate the body text content to the real subject matter: the apple pie. To help search engine to index the right content, we add in the metaTAGs field these keywords: apple, pie, recipe. Even if these keywords are the same as in the title of the page, search engines appreciate their presence and do a more efficient job to index the content of the page.
In StandardWeb you can insert many keywords as you want, just separated by space or commas.