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.’”