From what I have read (and seen on my Den)...the terminal leaf is the LAST leaf that grows on top of a particular cane on your Den (you probably guessed that from the name )
Anyway, the terminal leaf doesn't splay off to the side, near perpendicular to the plant, but actually grows up at an angle (on mine anyway, maybe different for others). There is also on mine, if you look down into the crown of the cane, a little nubbly looking thing that looks like an endcap (anyone...is there a particular name for this part of the plant?).
Anyway, that's my take on it...I am sure that someone else will probably give you a better explaination than mine.