The difference between focus keyphrases and meta keywords
The focus keyphrase field in Yoast SEO is specifically not the same as the meta keywords field in other plugins. By default, our plugin doesn’t give you a field to enter meta keywords, as meta keywords have been proven to be a waste of time.
The focus keyphrase (seen in the screenshot below) in the Yoast SEO plugin has a completely different purpose. This article on the focus keyphrase explains what the focus keyphrase is and what it does.