다녀올게 (casual) · 다녀올게요 (polite) · 다녀오겠습니다 (formal)
I'll be back; see you later (said when leaving home or the office)
Example
엄마, 저 지금 학교에 다녀오겠습니다!
Mom, I'm heading off to school now!
Word parts
다니다 'go about' plus 오다 'come': literally 'I'll go and come back'.
Good to know
The family replies 잘 다녀와 or 다녀오세요; it's a fixed daily ritual in Korean homes.