To be au fait is to be up-to-date and well-acquainted with something. When you’re au fait, you know something well.
This French term, which means “to the fact,” apples to those things you know plenty of facts about, especially current facts. A doctor should be au fait with medical advances. A quarterback should be au fait with different team’s defenses. This word has to do with current knowledge. If you haven’t watch a TV show for years, you’re not au fait with it. Being au fait is like being abreast, au courant, or up on.