This icon shows a graph with a normal "L" shaped line. On the graph there is a large curve which starts the graph at the very bottom, peaks at the top of the graph, then curves back down to the bottom. In the center, running horizontally, there is a dotted line to indicate the average value.
This is a Bell Curve icon. It is available in PNG and vector. Downloading is free for PNGs up to 100x100px.