To celebrate the Winter Tryst, Ai-Naidar wear no House sigils, no caste-marks, and no identifying colors. They strip their speech and don their masks, and even the cold is complicit, for it inspires the layers of enigmatic costumes. To the parks they fly, gaily-clad or somber, outrageous in anonymity. And there they mingle, dance, and couple beneath the trees, hoping for Winter's children to enrich their families.
The dances' moves and allowed touches are codified, but they are salacious in the extreme, all the more for never knowing whose hand flows over one's wrist, whose tail flicks against one's ankle, whose fingers trail over one's waist.
Winter's children are the end of the celebration, but not the reason for the "making the gift." Some Ai-Naidar even drink "until-a-better-time," a contraceptive, before celebrating the Tryst. Many don't conceive Winter's children until they're already married, or settled within their chosen roles.
The children born of the Winter Tryst are called Winter's children, and Ai-Naidari siblings will refer to such a child as a Winter-sister, or Winter-brother. I should look up the formal name, which I have somewhere.
On a practical note, with few exceptions, you are expected to marry within your caste. The Tryst was started, in part, to address the need to prevent inbreeding, but also to address the need to have a chance to be totally free of caste restrictions.