n Several different diseases of potato|potatoes producing pits and other damage on their surface, caused by Streptomyces -bacteria.
n Short form for common scab, a relatively harmless variety of 'scab' caused by Streptomyces scabies.
n (botany) Any one of various more or less destructive fungus disease|diseases attacking cultivated plants, and forming dark-colored crustlike spots.
n (context|founding) A slight irregular protuberance which defaces the surface of a casting, caused by the breaking away of a part of the mold.