Hack days are events where developers innovate and collaborate to solve problems using existing technologies in a 24-hour period. The document discusses that hacking means finding creative solutions regardless of limitations. It provides examples of historical innovations that were initially dismissed but later became mainstream products. The author encourages participants to identify issues and build working solutions by combining available online tools and frameworks. Presentations should demonstrate the hacks through live demos rather than slides and emphasize the problem solved over technical details. Participants are asked to publish their work publicly and continue collaborating with other hackers after the event.