Well to define its characteristics, I’d say that its an intellectual activity and obviously it is thinking of new ideas is not a piece of cake. It requires you to think out of the box.
Brainstorming is open and diverse its not about what is right or wrong but its more about what’s new and different. It involves creativity, as obvious as it is both creativity and innovation goes hand in hand.
Its usually done in a group setting, let’s say in offices people have a meeting to discuss about a project and to start it they all pen down their raw thoughts thinking openly about this new project.