放屁用英语可以说成 fart。它的来源来自于古英语 "feortan"，意思是放气、喷气。例如：

I heard a loud fart in the bathroom.

我在浴室里听到一声很大的放屁声。

She let out a fart when she sat down on the couch.

她坐到沙发上时放了一个屁。

Fart is a rather informal and colloquial term, and is not typically used in more formal or professional settings. It is also considered impolite to talk about farting in public, so it is best to use this term with caution and in appropriate settings.