Source : Webster's Revised Unabridged Dictionary (1913)

Au fait \Au` fait"\ ([=o]` f[asl]"). [F. Lit., to the deed, act,
   or point. Fait is fr. L. factum. See {Fact}.]
   Expert; skillful; well instructed.

Source : WordNet®

au fait
     adj : being up to particular standard or level especially in being
           up to date in knowledge; "kept abreast of the latest
           developments"; "constant revision keeps the book au
           courant"; "always au fait on the latest events"; "up on
           the news" [syn: {abreast of(p)}, {au courant}, {up
           on(p)}]