Gneiss is a type of high grade metamorphic rock which typically has a banded foliation. High grade in regards to temperature and pressure not mineralization.
Veins are minerals which have crystallized in void space in rocks. A stringer vein is a thin discontinuous vein.
A footwall is the rock beneath a dipping fault when viewed in cross section. If you have a dipping ore body it can also refer to the rock below the ore body as the foot wall.
