The efficiently warm (and convenient) method of intercourse, typically preferred after a hot beverage, requiring little to no removal of clothing for penetration to occur
"Baby I don't feel like it tonight, it's too cold".... "No worries, we'll just have winter sex"
"It's just winter sex, your pants won't go below mid-thigh"
"Boxers with the opening in front were made for winter sex"
"Alaskans are experts in the art of winter sex"