The number 20 is called a “score” due to its historical significance in counting and notation. A “score” is an archaic term that represents 20 units or items. The word “score” has been used for centuries and can be traced back to Old English. One of the most famous uses of the term “score” is in Abraham Lincoln’s Gettysburg Address, where he begins with “Four score and seven years ago,” referring to 87 years, or four times 20 plus seven.

Source: Geeks for geeks