Definition & Meaning of "know what is what"

What is the origin of the idiom "know what is what" and when to use it?

The origin of the idiom "know what is what" is not well-documented, but it is part of a broader group of idiomatic expressions related to knowledge and understanding. The use of "what is what" in this context suggests a clear understanding of the true nature or essence of something. This phrase is used to emphasize that someone possesses a deep understanding of a particular subject, situation, or set of circumstances. It implies that the individual can distinguish between what is true or important and what is not, making informed decisions or judgments.