Noun - 1. the bloody discharge of the uterine lining during the menstrual cycle. 2. the surprise left if one's panties when the monthly visitor arrives unexpectedly, so called because it resembles the topping on Costco's Berry Sundae.
Person #1: (eating something)
Person #2: It looks like you're eating berry sundae.
Person #1: hahaha... GRRRooooossssss!!!