Dutch door

A Dutch door (American English), stable door (British English), or half door (Hiberno-English), is a door divided in such a fashion that the bottom half may remain shut while the top half opens. They were known in early New England as double-hung doors. The initial purpose of this door design was to keep animals out of farmhouses or to keep children inside while allowing light and air to filter through the open top; essentially combining a door with a fairly large window. When the top half was open, they also allowed a breeze, but stopped the wind from blowing dirt into the house.