Other forms: flying buttresses
Though its name makes it sound like it's soaring through the air, a flying buttress is simply a supportive arch that sticks out from the exterior side of a wall. Flying buttresses are most commonly found on very old churches and cathedrals.
An arch that extends out from a tall stone wall is a flying buttress, an architectural feature that was especially popular during the Gothic period. The practical purpose of a flying buttress is to help hold the heavy wall up by pushing from the outside—a buttress is a support—but it also serves an aesthetic purpose. Notre-Dame cathedral in Paris is probably the most famous building in the world constructed with flying buttresses.