원곡임 is constructed as 원곡이다 + -ㅁ, meaning "(This/It) is the original song". * 원곡이다 = 원곡(original song;) + 이다(it is). * -ㅁ: suffix for verb-derived nouns (like gerunds in English). The -ㅁ form turns a verb into a noun, which shows up in three usages. 1. Some nouns nouns have been formed this way. * 살다(to live) + -ㅁ -> 삶(life); * 죽다(to die) + -ㅁ-> 죽음(death), * (꿈을) 꾸다(to dream) + -ㅁ -> 꿈(dream). 2. It is used to create a noun from a verb on the fly as needed. * 모든 일은 끝맺음이 중요하다: The finish is important in everything. 끝맺다(to finish) + -ㅁ -> 끝맺음(finish, finishing). (끝맺음 is not a common noun listed in the dictionary, but is used like one here) 3. It is also used as a sentence ending in informal contexts, or to quickly present the facts. * 이게 그노래의 원곡이야 -> 이게 그 노래의 원곡임 (This is the original version of that song). * 피의자는 17 시에 패해자와 만남 (Suspect meets the victim at the 17th hour). Having a curt, impersonal and business-like feel, this form is not appropriate in normal writing. It is however popular when presenting a list of low level facts, like in business presentations or long lists. It's also used a lot on the Internet in situations when both the polite and the casual ending feel a little awkward. One can avoid the awkwardness and also save space by using -ㅁ ending, but it is still stiff and unnatural sounding.