성명 어떻게 되십니까 - seongmyeong eotteohge doesibnikka

The mystery is .... formal or informal. 성함 is formal word, very polite word which you are showing your respect to the person you're talking. 이름 is informal which you can use to your friends or younger ones or to your self. If you say 내 성함은.... hahaha... very funny. Never, don't use it. Formal, polite or informal, casual. They are the one of keys to Korean language.

The mystery is .... formal or informal.
성함 is formal word, very polite word which you are showing your respect to the person you're talking.
이름 is informal which you can use to your friends or younger ones or to your self. If you say 내 성함은.... hahaha... very funny. Never, don't use it.

Formal, polite or informal, casual. They are the one of keys to Korean language.