What means "Five score years ago"? What means "score" in

What means “Five score years ago”? What means “score” in this phrase?

score - 20 years. Five score - 100.

President Lincoln gave the Gettysburg address (speech) that is the most memorable use of “score”. The Gettysburg Address by Abraham Lincoln

In general, that is an antiquated term that would not be used in everyday speech.

The speech that jreidy links to is very famous here in the States, and in other countries, too, if I am not mistaken. Students in American schools often have to memorize it for class. I know I did. Surely Dr. King’s intention in using the word “score” was to make his listeners recall Lincoln’s speech and the message of that speech.