as free as a bird意思是：自由自在，无拘无束

【例句】
But In fact, I like that feel of as free as a bird.
但事实上，我还是喜欢那种一个人自由自在的感觉！

You are free of constraints, making you feel "as free as a bird".
现在的你无拘无束，就像一只自由的小鸟。