clover是“三叶草”，但是 a pig in clover 可不是“三叶草中的猪”，引申为在自己所处的环境里很开心很满足。

【例句】
She has worked hard to bring home the bacon all year round. In the holiday, she settled into the chair with a glass of wine and a book, happy as a pig in clover.
一整年她都在努力工作，赚钱养家，放假了她很开心很满足的坐在椅子上喝喝红酒、看看书。

He is into sports, so he's as happy as a pig in clover to join the city community sports club.
他热爱体育运动，所以他很开心加入了城市社区体育俱乐部。