A French doorway[24] has two rows of upright rectangular glass panes (lights) extending its whole length; and two of these doorways on an exterior wall and with out a mullion separating them, that open outward with opposing hinges to the terrace or porch, are referred to as a French window. https://beckettgoua84184.national-wiki.com/661308/navigating_the_market_for_solar_cleaning_tools_opportunities_and_challenges