DVD/Blu-Ray grading scale (play side):

10 - Mirror surface looks new, perfectly clear of any abrasions, scuffs or marks. 

9 -  Disc may have one or two light marks but no more

8 - a few whispy marks or scuffs apparent 

7 - this disc will have some light marks that do not affect play - an average disc

6 - more pronounced marks on this disc that may affect play on cheap players

5 - perhaps one or two bad marks or pervasive scuffing that may affect play on cheap players

4 - Badly scuffed - will not sell at or below this grade level

3 - Trashed

2 - Arts and crafts project

1 - Hockey, anyone?