Heh, If we were in Texas, I'd be tempted to ask "Wuhl, where're YOU from?"
DiD is not a game, it's a style of play for a number of games. It's not the most popular style, but has quite a few adherents anyway in games like Morrowind, Oblivion, Skyrim, and the Fallout series. DiD stands for "Dead is Dead", and means just what it says. If your character is killed, that character is dead forever, and you have to start a new one. A DiD competition usually sets some parameters regarding characters, and the object is to see whose character accomplishes the most under those parameters before being killed off. That style adds a lot of excitement to events when you have many hours invested in a character and death starts looking probable in the near future.
Some people (like Diablo players) call DiD "Hardcore", although in other games that term has come to more often mean DiD with some kind of needs added in, like sleep, thirst, and hunger requirements. These kinds of things are used along with mods to keep old games fresh and exciting. I personally have thousands of hours in both Skyrim and Fallout 4, but in FO4 I've only finished one questline, and with 6,000+ hours in Skyrim, I've only recently finished some of the quest lines for the first time.
Well, probably a lot more than you wanted to know, but I hope that answers your question.