How is slide direction on windows and doors determined?

You may have heard the terms XO or OX used when talking to window and door companies. What this is determining is the slide direction of doors and windows. X is always the sliding panel (vent) of a door or window. O is always the fixed or non operable part of a door or window. Always looking at your home from the outside, an XO sliding patio door has the sliding panel (vent) on the left side and the O or fixed panel on the right. Just remember that you are always on the outside looking towards your home.