“Shooting wide open” has become a fad in recent years, with predictably patchy results. Cookery books seem obsessed by it, with depths of field so small that only one prawn on top of the seafood lasagne was properly in focus. But, however fashionable it may be, it’s very dangerous, especially at weddings.
“Wide Open” means that the lens is opened to its maximum aperture (the smallest f number). This lets the maximum amount of light through and results in the minimum depth of field. Most things in front of, and behind, the focal point will be progressively more and more out of focus. The house in the field here is an example of the opposite extreme. Shot at f18 on a bright day with plenty of light, everything is in focus and I still had enough shutter speed without needing to play games in Photoshop.