Translation:Singers are busy.
I was first introduced to Korean a long time ago by listening to 2NE1, and there's a song where she sings "nan babba (난 바빠)" and the translation (it even shows in the title) is "I'm busy". Is this an informal speech or something like that? I'm lost about the ㅡ that disappeared x)
난 is a shortened version of 나는 which is informal I. 바빠 is the informal conjugation of 바쁘다 to be busy. The ㅡ disappears because when a verb stem ends inㅡ it is conjugated following the rules of the vowel in the syllable before. The syllable has ㅏ so you replace ㅡwith ㅏ then take off the 다
That's the common distinction yes, but its an incomplete one. Topics can be singular and subjects can be general, it all depends in the greater context of the conversation. There is no explicit translation between definite and indefinite articles in English and topic/subject markers in Korean.