The excess weight a person gains over the course of the winter months. This normall starts around Christmas and progresses through January and February. People tend to gain winter weight when over holidays where food is abundant and also gain weight in order to survive in the cold weather. Winter weight is shedded during the spring time and is gone before summer.
Girl 1: Now that it's spring I've got to hit the gym.
Girl 2: I know. I've got to shed some winter weight if I'm going to be bikini ready for this summer.