A single image that is intended to give the reader an immediate understanding of the story or article's main message. The graphical abstract should be distinct from figures or diagrams in the rest of your article. It should be an overview as opposed to your results section. It should take less words to explain the graphical abstract than the actual abstract. Consult the journal's guidelines for size and structure.
Search #VisualAbstract in social media venues like Twitter and Instagram for examples.