sexual activity, sexual intercourse, sex
我特别讨厌成人用"性行为"这个词
I especially hate it when adults use the term “sexual behavior.”
— 朱诺 (2007)
死之前还有过性行为
They had sex before they died.
— 利维坦 (2014)
有性行为吗？
Do you have sex?
— 普通女人 (2017)