means A low protective wall or railing along the edge of a roof, balcony, bridge, or fortification, meant to keep people from falling and to shield defenders.

from From Italian 'parapetto,' literally 'protect the breast' — 'parare' (to guard or ward off, the same root that gives us 'parasol' and 'parachute') plus 'petto' (chest, from Latin 'pectus'). It entered English in the late 16th century through French, originally describing the breast-high battlements soldiers crouched behind.