the season after autumn and before spring, when the weather is coldest.——Longman Dictionary

The season between autumn and spring (generally regarded as lasting from December to February in the northern hemisphere and from June to August in the southern hemisphere), characterized by cold weather, long nights, the absence of leaves on deciduous trees, and the hibernation of certain animals. Also: the colder half of the year, including the cooler parts of spring and autumn, as contrasted with summer.——Oxford English Dictionary  @en