When a search engine spider crawls your page it’s looking at the content. By looking at your content, it can tell what the page is about and knows where to file it away in the search engine’s index. So, keyword targeting is very important. The Voltmeter returns 5 keywords. (Keywords and key phrases are the same thing- A “keyword” can contain several words.) It is basically looking at your site’s content and returning keywords that a search engine will likely think the site is targeting.
Optimizing page content with keywords is similar to walking a tight rope. You don’t want to go overboard and churn out unreadable junk because it’s poor usability, your site will just bounce users away and you’ll never get any links. But you do want to include various phrases in your text that poeple interested in your topic would search for. The golden rule here is to write for people first.