From Longman Dictionary of Contemporary Englishwhat’s whatwhat’s whatSITUATIONthe real facts about a situation that are important to know She’s been working here long enough to know what’s what. → what
Examples from the Corpus
what’s what• I am a fly on the face of the Almighty, crawling over the surface to see what's what.• He tells his mates what's what, and they laugh when he does.• I keep my ears open and I know what's what around the office.• So let's start by taking a look at what's what in floorcoverings.• What's what in the psychic world?• I like to think our academic standard's gone up, and we know what's what in the world. 