1. What does it mean?
황금막내 literally combines golden with youngest member. Fans use it as an affectionate compliment for a group's youngest member who seems capable in several areas. It is particularly associated with BTS's Jungkook, though the wording can be applied more broadly.
Also written or said as hwanggeummangnae
2. The nuance
This is a praise label, not an official job description or objective ranking. Being the youngest alone does not convey the multi-talented implication of 황금.
3. Examples
“노래도 춤도 잘해서 황금막내라는 말이 어울려.”
They're good at singing and dancing, so 'golden youngest member' fits.
“이번 무대에서 황금막내의 실력을 보여 줬어.”
They showed why fans call them the golden youngest member in this performance.
Sources
References support the meaning and usage. Example sentences are written for NoCapWiki.