Your school probably has a choir. Maybe you sing in it. And then, of course, know that there are one or two particularly vociferous participant boy or girl. They usually charge to sing the song then all together pick up. This is singer - soloist who performs solo songs, and the chorus picks up the chorus.
Over time, the word leader began to be used in a figurative sense. Now it is often used in the sense of a pioneer in some cases, the one who goes ahead and leads the other. This is not surprising. Because somewhere in the campaign, in difficult conditions, when the song is not a concert room, and the assistant, which encourages, adds strength, helps to move forward, Zapevalov is no one who is simply better, more beautiful voice. Singing a cheerful song the one who is stronger in spirit, who has the stronger will, who is able to overcome difficulties and carry forward.