Differences between the Vocals;

In every Kpop group -boy or girl groups- there is always a main, lead, and sub vocalist. Let's keep all of this short and clean.

A lead vocalist is someone who sings the most. Lead vocals is a good singer that help pad the song. The lead vocal is the second (next) vocally superior vocals. Lead vocals' role is to sing the majority part of the song and take the reigns in performance. The lead vocals leads the other members into the song. They usually are the ones that get the lines that change the pace of the song.

Now, the main vocalist basically is the best among the rest of the group. Main vocals are usually the stongest, most stable and best range singer in the group. They are in charge of high notes and/or belted notes. And usually, the main vocals are the one who sang in the background of the chorus. A main vocals sings a lot and have more challenging parts than the lead. The main vocals are tasked with (often) high notes towards the end of the song or the of the song. They are also the ones who are responsible for the adlibs. The main vocals does not necessarily sing majority of the song, however they have more lines than that of the sub-vocals. It is safe to say that if someone from the group do the high notes and adlibs, he or she is the main vocal.

Lastly, sub-vocalist, are the ones who support and backup during choruses or group parts. Their solo line usually last about five to seven seconds (less than ten seconds). In author's opinion, the sub-vocals are the ones whose voice aren't very strong and stable compared to the others.