V is short for Vanguard and Mundi can mean World or Universe. My particular meaning is Universe because the implication of the word Mundi for "world' actually has to do with what the people at the time thought all of existence was. So it's Vanguard Universe.
Fun story. Coming up with the name took forever. When I wrote a Yugioh blog, "Gameking League" just made sense to me. Yugioh translates as Gameking and I had a League of players in a group before I wrote that blog. V Mundi was very different because it was primarily a blog and at first I was against the idea of having a community. So without a communal intent, it couldn't have some sort of social representative word in it and I went with universe. The intention there was that it would be an Encyclopedia of Vanguard which was going to eventually be as all-encompassing as possible (hence universe). I didn't want to call it Encyclopaedia Vanguardia because I felt that was a bit complicated and pretentious.
One of the earliest names I started with was "Six Damage" which is the default and ideal win condition in the game. The idea came from the site "Six Prizes" which is for the Pokemon TCG. Ultimately, I decided on V-Mundi (with a critical symbol for an asterisk) instead but I still have plans to use Six Damage for the name of a podcast or something similar if I can ever find the time and equipment to do it.