A referral program has two levels. It means that partners can engage referrals, and those referrals can become partners as well.
Besides a general commission to a partner for an order of his referral you can assign a commission for an order of a two-level referral partner. You can do it for all partners or for a certain partner.
Thus, if a partner A engages a partner B, then a partner B engages a partner C,
the partner B receives a commission for an order of the partner C
the partner A receives a commission for the same order in terms of commission for two-level partner.