Period of dormancy in animals during winter months is called aestivation/hibernation.

Explanation

**Step-by-Step Solution:**

1. **Understanding Dormancy**: Dormancy refers to a state in which an organism becomes inactive or goes into a period of rest due to extreme environmental conditions, such as very cold or very hot temperatures.

2. **Identifying the Type of Dormancy**: In the context of winter months, the specific type of dormancy that occurs is called hibernation. During hibernation, animals enter a state of reduced metabolic activity to conserve energy.

3. **Characteristics of Hibernation**: Animals that hibernate typically find a safe place to hide during the winter months where they can endure the cold. They also store food in the form of fat in their body tissues to sustain themselves during this period of inactivity.

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