In every group there must be a leader. Even in the birds like the geese, they have their leader especially in migration process. The leader is the one who guide the group on the direction they are taking. He is the one who represent the group as a whole. Whatever he does it should be for all of the members of the group. In a band there is also the leader which is called the lead singer or vocalist in terms of popular music. This position is called frontman in terms of rock music. Sometimes he may play an instrument.
When it comes to rock and roll the lead vocalists perform the main part and chorus is sung by group members that are called backing vocalists. This can be seen also in gospel music or soul music performances that there is the lead vocalists and sing specific main lyrics being supported only by the members. Groups can number into ten or 30 or even 100 performers. Some plays instruments and some do the backing vocalists.
The lead singer role is very important as he is considered the face of the group. His voice is the one that they follow and listen. In a band composing four members, they only have one lead singer. All other members play instruments. Though they have the part in their performances that they show their talent in instrument still the lead vocalist is the main.