Description of 20/80 scout scale:
The Scouting Scale works from 20-80, with 50 being Major League Average. The scale operates loosely on a bell curve, so the further you move from 50 the fewer grades you'll find among ML players (e.g. Justin Verlander's fastball, Ichiro Suzuki's arm strength, Mark Reynold's power and Albert Pujols' hit tool would all be 80 grade). A 60 grade is sometimes referred to as plus and a 70 grade is sometimes referred to as plus-plus.
Scout to prospect grading scale with descriptions:
66 and over / A+ / Potential top prospect in baseball; potential generational talent
63-65 / A / Elite prospect; perennial all-star candidate
59-62 / A- / Top tier prospect; above-average first division starter; front end starter
55-58 / B+ / Good prospect; first division starter; mid-rotation starter; top tier reliever
51-55 / B / Solid prospect; second division starter; back-end starter; good relief arm
46-50 / B- / Prospect with questions; fringe starter; useful bench player or platoon; fringe reliever
40-45 / C+ / Flawed prospect; fringe bench player
35-39 / C / Significantly flawed prospect; limited utility; AAAA placeholder or injury insurance
30-34 / C- / Fringe prospect; significant hurdles to Majors
20-29 / NP / Non-prospect; organizational player