Although the search function does yield dozens of results mentioning duping, I did not come across any results that specifically explain what duping is. I searched exactly what the OP asked: "what is duping".
I, myself do not need to know what duping is, I already know. I just wanted to illustrate that when a haughty, holier-than-thou forum member hastily tells a newcomer to use the search, that it doesn't always provide the answers one may be looking for.
