Remember when the word, window, only referred to an opening in a wall covered with glass. Now the space program changed all that. A window is still an opening, but the folks at Cape Canaveral referred to that brief period of time where everything is right for the launch. The wind is okay. The weather is okay. They checked it at the Cape. They checked the down range. The atmospherics are okay for communication. The conditions have been projected for the time of return and they look good. But the window will pass soon. If you're going to get it off the ground, go when the window is open.