란 걸

that ... is/are

→ 이다
phrase Rare #25,356
that ... is/are A conversational contraction of -라는 것을, used after a noun to express “that it is...” or “the fact that...”.
KO: 그 사람이 거짓말쟁이란 걸 알았어요.
EN: I realized that person is a liar.

아빠 얘기 란 걸 알겠어요

I understand that you're talking about Dad.

— 추락의 해부 (2023)

우리 아빠 란 걸 어떻게 알아?

How do you know he's my dad?

— 리턴 (2003)