... it's short for "Pokémon Go outside where their main demographic is woefully unfamiliar with the surroundings".
Since my older son has been playing Pokémon for many years, I felt like I should see what Pokémon Go was about. The first night it was available, I loaded it onto my phone, and after a little bit of user information setup, it puts up a map of our neighborhood with locations of a few Pokémon nearby. I took my older son outside with me, we turned the camera part of the game on, and we looked at the screen where it shows what we currently refer to as "augmented reality" or AR. I flicked a representation of a Pokéball at a representation of a Pokémon that somewhat seemed to be out in the neighbor's yard. (I'm sure that he didn't know that he had a Pokémon infestation.)
I know that I'm not really the intended audience for the game, so it's no big loss if I'm not playing it. My son doesn't have a smartphone, so he's not playing it. The game vaguely reminded me of a location-based game that was out a few years ago that one of my other neighbors wanted me try, but I didn't have a smartphone then (and frankly I was a little suspicious about the nature of a game that was GPS tracking you and all of your friends). For all I know, that game was Niantic's previous game - Ingress. It didn't have Pokémon, it just had a map with little lights all over it and it used local landmarks as control points for a team vs. team resource collecting game. While it didn't take off like Pokémon Go has, it was a good showcase for the location-based technology and apparently helped them better map places for Pokémon Go.
The Nintendo DS/3DS family couldn't play Pokémon Go because although it's fully capable of integrating the camera into AR-type games, it's only able to communicate with the internet via WiFi and doesn't have any sort of mobile data connection. (Honestly, I don't use the mobile data on my phone that often, so that was another strike for me against Pokémon Go.) Also, other than the handful of AR games that come with the DS/3DS systems, most developers have ignored AR gaming in favor of more traditional games. Also, all of the Pokémon games on Nintendo's handhelds have all had much more complicated mechanics (battles, RPG elements, interacting with NPC's) than Pokémon Go does.
I'm a little bit surprised that some adults have taken to Pokémon Go as much as they have, but I can only assume that's because they either haven't played any sort of AR game before, they're nostalgic for Pokémon, or they just needed an excuse to get outside and didn't have one.
I'm not surprised at all that kids (and some adults) have had odd discoveries and mishaps playing Pokémon Go. Most people these days aren't used to being pedestrians for any length of time, and the random distribution of the Pokémon may cause people to walk places that they otherwise might not go. This is made grossly more difficult by the fact that you're staring through your phone screen which effectively narrows your field of vision, and creates much lower situational awareness than you would normally have as a result.
Well, don't worry. Soon enough, we'll have the first mishaps with people playing Occulus Rift outside.
Happy Pokémon hunting to those of you who are, but be safe out there. To the rest of you, just remember that if you think that Pokémon Go is stupid, then you're probably not in the intended demographic.