Generally it is the the handles, a pot has 2 and a pan has one...It could also be considered the depth of it. Pots are generally deeper and have steeper sides than pans
A Wok has much higher sides, allowing food to be "tossed" whereas a frying pan has shallower sides, which doesn't allow "tossing" (without emptying the contents all over the stove)
An angel food cake pan is usually circular and shaped sort of like a dome or a bundt pan. A pound cake is typically baked in a loaf pan, similar to that of bread.