A French door[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 no mullion separating them, that open up outward with opposing hinges to a terrace or porch, are generally known as a French window. https://beckettgoua84184.national-wiki.com/661308/navigating_the_market_for_solar_cleaning_tools_opportunities_and_challenges