The phrase "au fait" is a French term that is often used in English. It is an adjective that means being knowledgeable, well-informed, or up to date on a particular subject or situation. When someone is "au fait" with something, it means they are familiar with it and aware of the latest developments.
In summary, "au fait" is a useful term in English that describes someone who is well-informed and aware of the latest developments in a particular area.