A sconce is a wall-mounted candle holder or light fixture. The hallway in your house might be lit by an electric sconce on the wall.
The noun sconce can be used in two ways. First, a light that hangs on a wall is a sconce, whether it's an electric light in a wall bracket or a flaming torch mounted in a castle's corridor. The other kind of sconce is a castle or city fortification that's meant to protect against both enemies and bad weather. Both kinds of sconce come from the Old French esconse, "lantern or hiding place," with the Latin root abscondere, "to hide."