"Diddly squat" is an American slang term that means "nothing at all". It is thought to have originated in the 19th century, and it is believed to be a corruption of the phrase "diddly-squat", which was used in the 17th century to refer to a small amount of money. The term "diddly" was also used in the 19th century to refer to a small amount of money, and the term "squat" was used to refer to a small piece of land. So, the phrase "diddly squat" is thought to have originated as a way to refer to a very small amount of something, and it has since come to be used to mean "nothing at all".