what's what

what's what

slang The true facts or most fundamental information (about someone or something). After putting it off for a week, Sarah finally told Jane what's what and ended their relationship. I think it's about time that you knew what's what about how this business is run.
See also: what
Farlex Dictionary of Idioms.

what’s ˈwhat

(spoken) what things are useful, important, etc: She certainly knows what’s what.
See also: what
Farlex Partner Idioms Dictionary

what's what

Informal
The fundamentals and details of a situation or process; the true state or condition.
See also: what
American Heritage® Dictionary of the English Language, Fifth Edition.

know what's what, to

To be cognizant of the full situation; to be familiar with all the facts. This term may have been coined by Samuel Butler (Hudibras, 1663): “He knew what’s what, and that’s as high as metaphysic wit can fly.” Dickens’s Sam Weller (Pickwick Papers) used it too: “‘That ’ere young lady’, replied Sam. ‘She knows wot’s wot, she does.’”
See also: know
The Dictionary of Clichés by Christine Ammer
See also:
  • (Now) where was I?
  • be no love lost between (two people)
  • talk to the hand
  • talk to/tell it to the hand
  • be little love lost between (two people)
  • breeze up to (someone or something)
  • correspond
  • correspond about (someone or something)
  • (I) wouldn't want to be in (someone's) shoes
  • stock in trade