What is the difference between a mullion and a muntin?

A mullion is the bar or bars in the middle of a window. A muntin is the bar on the outside of the window. == I have heard much debate about this question this is how I understand it. A window sash is made of the stiles, rails and muntins. The rails being the top and bottom and the stiles the sides that ride in the jamb, the muntins are the thin pieces of wood that divide the sash into lites. There is a small lip on the back of the muntin that the panes of glass are bedded to then glazed. Mullions are the vertical trim pieces that divide the Windows in a ganged window, for instance a triple window would have two mullions separating the middle window from the outer Windows.