It's Duck Tape. It even has a cute picture of a duck on it. it started out as ducted tape but over the years people started calling it duck tape and it became a brand of tape.
^lies. It's definitely duct tape. Just check wikipedia!
It doesn't matter what you want to call it. In the USA they use both, and the least you could do is give a link. http://en.wikipedia.org/wiki/Duct_tape