What sort of icon/graphic could represent 'concept'?
It would be very helpful as a place-holder when I am making basic sketches and notes.
Third Party Edit (from comments):
hhajemi (OP): From my experience, I will normally try to clarify some key concepts in the areas of interest and the following discussions will be based/built/developed upon these concepts. Than the light bulb or CFL (thanks koiyu for sharing this) moment, I can use a "brick" or "jigsaw" piece to represent a concept. I believed that this is not original but I think it can serve the purpose. Thanks all for commenting.