First of all, a quick (well, 4 minutes or so) look at hipsters through the eyes of Levni Yilmaz:
Anyway, as far as I can see, being a 'hipster' more or less involves being opposed to mainstream culture and embracing lesser known or underground media, as well as often being in a state of being permanently ironic about everything. It is important to note that this is generally done for the sake of status rather than an actual deep enjoyment of these activities, just as much of the mainstream culture they reject is rejected solely for the sake of it being mainstream.
Unfortunately, it's a meaningless word nowadays, as most people who are labelled 'hipsters' on things like internet forums just tend to be people with a contrary opinion to what is popular, often for valid reasons. So, someone who doesn't like Skyrim may be labelled a hipster, because people assume they don't like it for the sake of being 'different' rather than actually finding the game flawed.