6-3-5 brainwriting is a type of idea-generating activity. It's one way to help a group come up with new ideas!
In 6-3-5 brainwriting, everyone in the group writes down 6 ideas on a piece of paper. Then everyone passes their paper to the person on their left. Then everyone reads the ideas on the paper they just got, and writes down 3 of their own ideas that build on the ideas from the first paper. Then everyone passes their paper to the left again. Finally, everyone reads the paper they just got and writes down 5 of their own ideas.
Basically, you keep passing the paper around the group and adding ideas until you have lots of ideas to work with! This is a great way to come up with creative solutions to a problem or interesting new ideas.