I was recently asked by a viewer to explain the concept of 두음법칙, and that's when I noticed there weren't yet any videos about it in English.
두음법칙 is a set of rules for how to read Hanja words - specifically it's for when the Hanja word begins with the letters ㄹ or ㄴ. This is a specific case, but happens frequently when reading Hanja words using Korean. It is why the word 여자 isn't read as 녀자 despite the Hanja word for 女 being read as 녀, and also why 소녀 isn't 소여. It's why 용 ("dragon") isn't read as 룡, when the Hanja word is 룡.