A flock of birds, sheep, or goats is a group of them.

You can refer to a group of people or things as a flock of them to emphasize that there are a lot of them.

If people flock to a particular place or event, a very large number of them go there, usually because it is pleasant or interesting.

A clergyman's flock is the group of Christians who come to his church or live in the area that he has responsibility for.