A hackathon is a short event where teams build something that works, often within 24 or 48 hours. The goal is functioning software or hardware by the end. At the end, each group usually presents what it built.
In June 1999 Sun Microsystems used the word for an event at its JavaOne conference. There Sun’s John Gage challenged attendees to write a Java program for the new Palm V. Facebook’s Like button was conceived at a hackathon.