Final answer:
The phrase "five score years ago" refers to a period of 100 years and is similar to the phrase "four score and seven years ago" used by Abraham Lincoln in his Gettysburg Address.
Step-by-step explanation:
The phrase "five score years ago" originates from a historical speech. A score is an old term for the number twenty, so "five score" refers to five times twenty, which is one hundred years. One of the most famous uses of the term "score" to denote a period of years is in Abraham Lincoln's Gettysburg Address, where he used the phrase "four score and seven years ago" to reference the time passed since the Declaration of Independence, totaling 87 years at that time.