Q: What is pecking order?
A: "Pecking order" is the social hierarchy of the chicken flock. Those at the top of the pecking order get the best nesting spots and roosting spots, for instance... and those at the bottom get what's left.
Small flock with plenty of space
This arrangement works out well so long as there is plenty of space on roosts, in nests, and plenty of food and water for everyone. If there is not enough, then the girls at the low end get picked on, and may not be getting enough to eat and drink. Always make sure your chickens have more than enough space and plenty of sustenance for everyone.
The other important thing to remember is that introducing new birds into an established flock will shake up the existing pecking order, and throw everyone into chaos. Read the related questions below to learn how to safely introduce new birds into an established flock.