Figure 3, Member Generation and Level Numbers illustrates the following parent, child, and sibling relationships:
A parent is a member that has a branch below it. For example, Margin is a parent member for Sales and Cost of Goods Sold.
A child is a member that has a parent above it. For example, Sales and Cost of Goods Sold are children of the parent Margin.
Siblings are child members of the same immediate parent, at the same generation. For example, Sales and Cost of Goods Sold are siblings (they both have the parent Margin), but Marketing (at the same branch level) is not a sibling, because its parent is Total Expenses.