Which characteristic of life describes: why you would shiver and get
goosebumps when it gets cold out

Answer:
Homeostasis
Explanation:
Living systems will always try to maintain homeostasis: a steady state of all internal and external conditions.
This includes body temperature and fluid balance.
Shivering and getting goosebumps are attempts the body makes to warm itself up, which means it is trying to maintain homeostasis.