A summary gives a short overview, or the main points, of something longer. She talked for days about the 800-page romantic novel, but her boyfriend's summary was "Girl meets boy, boy meets girl, boy rides horse into sunset, girl meets new boy. The end."
Summary is a noun, and "summery" is an adjective, but they sound alike and both describe something short. A summer feels like a short piece of a long year, and a summary is a short statement about a longer piece. When a long speech or writing needs retelling in a short amount of time, a summary conveys the meaning in fewer words. Often a book cover has a summary of what's inside, and an introduction has a summary of the main points in a chapter.