How do you say evening in Korean?

The most common way to say "evening" in Korean is 저녁 (jeonyeok). This refers to the evening time period itself. If you're saying "good evening," you would use a more formal greeting depending on the context, like 저녁 잘 보내세요 (jeonyeok jal bonaeseyo) which means "have a good evening" (polite).