The phrase "threescore and 10" means "70." It is used in the Bible in Psalm 90:10, which says, "The days of our years are threescore years and ten...." A score is 20, so three 20s plus 10 is 70.
Seventy is a symbolic number in the Bible, the result of two numbers that indicate completeness or perfection in Scripture: seven and 10. Seventy years symbolizes a complete lifetime. Other Biblical references to "threescore and 10" exist elsewhere in the Bible not related to age. Moses said in Deuteronomy 10:22 that threescore and 10 people (Israelites) went into Egypt. Judges 8:30 says that Gideon had threescore and 10 sons with his many wives.