What does four score and ten mean and where does the term 'score' come from?

Answer = 90.

Four score and ten refers to years. A 'score' is twenty, so four of them would be 80, plus ten, it's 90. The term 'score' was used in the bible and in famous speeches.

Answer

The word score originates from Old English scoru "twenty," from Old Norse skor "mark, tally", in the sense of say, a shepherd making a mark on a tally stick when counting sheep. Its use in the Bible is simply that of a common word at the time of translation then falling into disuse though language change.