As a rule, private parties, corporate parties either (for employees of an organization or community) or a proper party "for his." As a rule, such activities clearly defined by their focus whether the presentation of a new product or simply meeting hangouts. Design can be very different depending on the above, sometimes it's a small dance floor in luxurious apartments, bars, places for recreation, swimming pools, sometimes abandoned power station or even equipped place in the woods. Most importantly, there is nobody outside, people are not in the topic etc. So if you are invited to a live parties, rest assured that I met there are close to you in spirit (even strangers) people. Among the guest musicians or DJs may well be a world-class celebrity, who never met a lineup of official events. That's what this kind of underground.