Idea of Concept Icon
This is a picture to represent "concept". This icon is made by starting with a square. Inside the square are two double sided arrows. One on the left hand side and one at the bottom. There is a light bulb in the image on the top right hand side boxed in by the arrows.
This page shows the different variations of the Concept from an Icons8 icon pack. Feel free to resize and recolor the icon, and then download the icon in PNG format for free.