People interested in a certain topic (like robotics, or games, or health, or computer music, or… your favourite topic) come together, with computers and the necessary material, and build together programs, robots, games, apps for sports or to support sick people, music, … on a given day.
The word is a combination of
– “hacking”, which in the computer community means “getting things done” (and also braking into systems, but that’s the very negative achievement of those who hack someone else’s systems)
– and marathon, because typically Hackathons are organised to a full day, and some even 24 hrs or longer.
Together it’s more fun to work, and one can meet a lot of like-minded people who one would not have met without the specific gathering.