Winter Wolves are a species of magical beast/monstrosity hailing from Dungeons & Dragons and, by extension, Pathfinder. As their name suggests, Winter Wolves are magical wolves distinguished by their "wintery" power set -- they are traditionally immune to cold, can exhale a frigid breath weapon of some kind (either a cone of cold or a ranged projectile), and sometimes can do bonus cold damage with their bite attacks. Distant relatives of Worgs (the D&Dification of Wargs), they share their cousins' traits of being gigantic wolves with human-level intelligence and even, sometimes, the ability to speak.
Adventure Path #68 -- Reign of Winter Part 2: The Shackled Hut tells us more about Winter Wolves than anybody cared to know. In Irrisen, they were part of Baba Yaga's armies and helped conquer the region. In return, they were given their own town, Redtooth. In both Redtooth and the Howlings district of the Capital Whitethrone, an enchantment allows the wolves to take Human form. This also happens to allow Winter Wolves to take human mates, if they're so inclined. And yes, under these conditions, Winter Wolves can breed with humans. Such pairings always bear Winter Wolf cubs; Human mothers actually grow fur and wolf-like features during the prengancy, which are shed in the following weeks(should they survive the birth).
Why is all this given? Well, in the adventure itself, the party has to enter Whitethrone from the Howlings sector. Earlier in the module, the party likely killed a particular Winter Wolf and had it's fur come off as a magic item known as a Rimepelt that allows the wearer to transform into a Winter Wolf. Chances are, the Rimepelt-wearing PC will end up drawing the amorous attentions of Greta, a Winter Wolf guarding the Howlings entrance. The setup is too good for most GMs to pass up, and so most of them try to steer the party into getting Greta's attention.