Final answer:
Seasonal affective disorder (SAD) is a type of depression that occurs most often during the winter months. It is characterized by symptoms such as increased appetite and sleepiness, and is more common in regions with long winter nights.
Step-by-step explanation:
The type of depression that occurs most often during the winter months is known as seasonal affective disorder (SAD). This mood disorder is characterized by symptoms such as increased appetite, sluggishness, increased sleepiness, and a tendency to withdraw socially. It is more common in regions with long winter nights.