what's what

• what is what

what's what (uncountable)

1. (idiomatic) Precisely what the situation really is or what the facts truly are.
   • 1823, Lord Byron, Don Juan, Canto the Tenth:

     Besides, he had some qualities which fix

     Middle-aged ladies even more than young:

     The former know what's what; while new-fledged chicks

     Know little more of Love than what is sung

     In rhymes . . .

   • 1918, P. G. Wodehouse, Piccadilly Jim ch. 18:

     "Well, I know what's what, too. I know what you are for one thing." He chuckled. "I've got your number all right."

   • 1921, Samuel Hopkins Adams, Success ch. 17:

     Anyway, he's a wise old bird and may hand you a pointer or two about what's what in New York.

   • 2011 Aug. 15, Sonia Van Gilder Cooke, "Sangat TV," Time:

     Sometimes it takes a scruffy underdog to show the professionals what's what. During the London riots, it was tiny Birmingham broadcaster Sangat TV that trumped the BBC and CNN with its riveting footage and quirky commentary.

• Not uncommonly used in circumstances in which someone is correcting erroneous information or dispelling ignorance.

• set straight
• who's who