Brainstorming is gathering raw material. Concept development is turning that raw material into something that stands.
In a brainstorm you look for direction, associations, energy. You finish with two or three clusters that have movement in them.
Concept development begins after that: you choose one direction and build it out into a core idea. Then you write the narrative thread and think about venue, programme and experience.
The brainstorm takes a few hours. Concept development usually takes one to two weeks. With us, one flows into the other. The brainstorm facilitator takes the output to the concept team. That team works on it further over the following days.