Barcamp is a tech oriented unconference which is organized by the attendees for the attendees. It is an event where people in the tech community come together to share ideas, knowledge, experiences with each other to benefit from the collective wisdom of peers. There are no attendees and no speakers, only participants. Everyone contributes in some way or other.
Here’s a slide deck, by one of organizers of Barcamp Delhi 8, about what is Barcamp & what to expect from it.