Complex sentence: Shelf-stable food (sometimes ambient food) is food of a type that would normally be stored refrigerated but which has been processed so that it can be safely stored in a sealed container at room or ambient temperature for a usefully long shelf life.
Split into simpler sentences: Shelf-stable food (sometimes ambient food) is food of a type that can be safely stored at room temperature in a sealed container. This includes foods that would normally be stored refrigerated but which have been processed so that they can be safely stored at room or ambient temperature for a usefully long shelf life.