What do we call the defensive openings in castle walls for archers?

The story behind the answer

These narrow, vertical openings in curtain walls and towers let archers or crossbowmen shoot out while staying protected. Unlike murder holes—downward-facing openings in gatehouse ceilings for dropping stones or boiling liquid—these face outward. Crenels are the open gaps atop a parapet between merlons, and battlements are the whole parapet (merlons plus crenels), not the wall openings themselves.

Often called loopholes or arrow slits, they were cleverly engineered with splayed interiors that widened inside the wall, giving defenders a broad field of fire from a tiny exterior target. Designs evolved into cross- or keyhole shapes to suit crossbows and early firearms, and their placement created interlocking fields of fire along approaches to gates and walls, a hallmark of medieval defensive planning.