:p
It's a nicer way of saying "unoriginal."
But, honestly, there's nothing
wrong with derivative per se as long as this particular derivation is done well (I think that Shutter the original is a great example - while it's a completely derivative JA ghost movie, I found the direction and acting clean with a lot of good jumps to it).
If your film is going to borrow from other films that came before, just make sure that it's a true derivation... Otherwise, see how you can make it stand out from its predecessors.