The POPPER or CRACKER is string or thread that has a bushy end that makes the pop.
The FALL is a single strip of leather (the narrower the better).
The THONG is 8-16 strips of leather woven around a center (which in a good whip is actually another mini-whip woven of 4-8 strips of leather)
The HANDLE differs between styles of whips (Stockwhip, Bullwhip, etc.) usually either a wooden handle or flexible cane stick, either bare or wrapped in leather.
The BELLY is what is inside the braided thong. In a good whip this will itself be braided leather, but in a cheaper whip it may be strips of leather or rawhide, or even rope or paper.
The KNOT is the knob on the end of the handle.