In one sentence, Barcamp is an ad-hoc gathering of people who love to learn and share, and more than anything they want an open environment where they can perform those freely.
So it is an event where you come to share your opinions and learn from others. Your topic of interest can be anything. Although the first Barcamp was related to more technical and geeky topics, but now over time they have expanded. Now you can talk about anything starting from Olympics to Human Rights, from assembly language programming to Natural Language Processing, anything!
BarCamp is an international network of user-generated conferences (or unconferences) primarily focused around technology and the Web. They are open, participatory workshop-events, the content of which is provided by participants. The first BarCamps focused on early-stage web applications, and were related to open source technologies, social software, and open data formats.
The format has also been used for a variety of other topics, including public transit, health care, education, and political organizing. The BarCamp format has also been adapted for specific industries like banking, real estate and social media.