In order for a window to be considered a window, it must be one that can used if a need arises. The requirements are a window must have large enough to be an emergency escape or rescue opening.
In Texas, we do not have many basements but we have a few. With that said basements, habitable attics and every sleeping room shall have not less than one operable emergency escape and rescue opening. For those homes that have a basement that contain one or more sleeping area, an emergency escape and rescue opening shall be required in each sleeping room.
An emergency escape or rescue opening shall open directly into a public way or to a yard or courtyard that opens to a public way and must have a net clear opening of not less than 5.7 square feet and a net clear height opening shall be not less than 24 inches and net clear width shall be not less than 20 inches. Lastly, where a window is provided as the emergency escape or rescue opening, it shall have a window sill height of not more than 44 inches above the floor