what's what

Noun

 * 1)  Precisely what the situation really is or what the facts truly are; the true state of things.
 * 2) * 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 . ..
 * 1) * c. 1925-29, (translator),, , Part I, chapter xvii:
 * This was a hardship in as much as inquiry showed that even in vegetarian restaurants many courses used to contain eggs. This meant that unless I knew what was what, I had to go through the awkward process of ascertaining whether a particular course contained eggs or no, for many puddings and cakes were not free from them.
 * 1) * c. 1925-29, (translator),, , Part I, chapter xvii:
 * This was a hardship in as much as inquiry showed that even in vegetarian restaurants many courses used to contain eggs. This meant that unless I knew what was what, I had to go through the awkward process of ascertaining whether a particular course contained eggs or no, for many puddings and cakes were not free from them.

Usage notes

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