Sum • mer /sŭm′ər/ n. 1. In the Northern Hemisphere, the usually warmest season of the year, occurring between spring and autumn and constituting June, July, and August. In the Southern Hemisphere, it constitutes December, January, and February. 2. A period of fruition, fulfillment, happiness or beauty. 3. The quirky girl, unlike any other person you'll ever meet. The most honest women in your life. Spontaneous, carefree, seductively beautiful in the most natural way. She is a man's last love because any women after that will never compare.