Actually it was originally named duck tape:
The first name for Duct Tape was DUCK. During World War II the U.S. Military needed a waterproof tape to keep the moisture out of ammunition cases. So, they enlisted the Johnson and Johnson Permacel Division to manufacture the tape. Because it was waterproof, everyone referred to it as duck tape (like water off a ducks back). Military personnel discovered that the tape was good for lots more than keeping out water. They used it for Jeep repair, fixing stuff on their guns, strapping equipment to their clothing... the list is endless.
After the War, the housing industry was booming and someone discovered that the tape was great for joining the heating and air conditioning duct work. So, the color was changed from army green to the silvery color we are familiar with today and people started to refer to it as duct tape*. Therefore, either name is appropriate.
Today, Duck® brand Tape is manufactured by Henkel Consumer Adhesives.
http://www.ducttapeguys.com/duckvsduct.html
Gaff Tape (also Gaffers Tape): This special grade of duct tape (often colored black) was developed by the entertainment industry to hold lighting equipment and cables in place and has a dull finish so that it wont reflect lights. Gaff Tape also has a specially formulated, less tacky adhesive that wont leave a residue when it is removed.