Coin history
What the Sheldon grading scale means
Dr. William Sheldon created the 1 to 70 scale in 1949. A coin graded 70 is considered perfect under the scale, and 60 and up is generally called uncirculated.
Grades are shorthand for wear and marks. Two coins with the same grade can still look different, so the grade is a starting point, not the whole story.
Letters before the number, such as MS for Mint State or AU for About Uncirculated, describe the coin's condition in a general way.