Hello, sorry this is a little late.
I believe the correct answer to your question, "an animals long period of inactivity during winter is called what" would be Hibernation.
Hibernation is when some animals (examples would be bears, and wild rabbits) sleep throughout the entire season of winter, when the temperature is too cold for them. They spend time before hibernation usually stocking up food, and creating a warm place for them to stay.
Hope this helps, and have a great day! :)
