Winter is the coldest season of the year in polar and temperate zones (winter does not occur in most of the tropical zone). It occurs after autumn and before spring in each year. Winter is caused by the axis of the Earth in that hemisphere being oriented away from the Sun.
In many regions, winter is associated with snow and freezing temperatures. Snow also affects the ways animals behave; many take advantage of the insulating properties of snow by burrowing in it. Mice and voles typically live under the snow layer.