Sexual act or intercourse. Often used in medical, legal, or educational contexts.
未成年との性行為は法律で厳しく禁じられている。
Sexual activity with minors is strictly prohibited by law.
感染症予防のために、性行為では適切な保護が重要だ。
Appropriate protection during sexual activity is important to prevent infections.
同意のない性行為は犯罪と見なされる。
Non-consensual sexual activity is regarded as a crime.