When it comes to food, there are three categorizations. A sandwich is any food which is attempting to be contained, but still has at least one open face. A calzone is any food which is attempting to be contained, but has no open faces. Finally, a salad is any food which does not attempt to be contained. This is officially known as The Grand Unifying Theory of Food Categorization.
This is the basis for your typical sandwich. It is clearly making an attempt to be contained, and has at least one open face. You can only see part of the ingredients.
This is the basis for your typical calzone. It is clearly making an attempt to be contained, and has no open faces. All of the ingedients are concealed within the containment apparatus.
This is the basis for your typical salad. It is not attempting any sort of containment. All ingredients can be seen clearly.