What does steamed bun bud mean?

The so-called steamed bun woman has a special lower body structure that can make men ecstasy during sex. This kind of woman will only appear once every few hundred years. Wan Yanxuan said that every few hundred women will appear. Years ago, in order to fight for a woman with a steamed bun and a bud, emperors from more than ten countries launched a war. It's like a world war. Every emperor wants to have such a woman to pamper him for the rest of his life.