whisker

A spontaneous columnar or cylindrical filament, usually of monocrystalline metal, emanating from the surface of a finish.

NOTE Whiskers are not to be confused with dendrites, which are fern-like growths on the surface of a material, formed as a result of electromigration of an ionic species or during solidification.

References: 

JESD22-A121, 10/05
JESD201, 3/06