The pyramid is a way to explain the different levels of quality of research.  The pyramid shows the different publication types for evidence based practice.  The higher up in the pyramid you go the better the quality of the research.  The box on the right defines the different types of resources.  The box further down shows you what databases have which level of resource in them.

Kysh, L. (n. d.) .Evidence pyramid : Publication types [Infographic]. University of Southern California. https://www.slideshare.net/slideshow/keck-year-2-evidence-based-medicine-guidelines/31852755#2