A Chaostreffen is a meet-up for people who feel somehow connected to the Chaos Computer Club.
The Chaos Computer Club is a large european association of hackers.
The activities within the CCC range from technical research and exploration on the of the technological universe through campaigns, events, policy advice, press releases and publications to the operation of anonymizing services and means of communication. The association consists of a series of decentralised local clubs and groups which organises regular events and meetings. The CCC conveys it's concern about various publication channels and always tries to talk to technically and socially interested and like-minded people. It follows the hacker-ethic.