Oh sorry, my bad. I'm always confusing "stove" and "oven". I looked it up at Pons http://is.gd/7bTRgh and when it showed "oven cooking" I mistakenly interpreted it to mean "cooking on the stove". So, next try: normally, "Topf" is used for the deep things you put on your stove and fill them with water for cooking. "Pfannen" are flatter items like a frying pan.
An image says more than a thousands words: see here:
EDIT: I've uploaded both articles to the immersion section :)