Some advertisers offer multi-tier programs that distribute commission into a hierarchical referral network of sign-ups and sub-partners. In practical terms, publisher "A" signs up to the program with an advertiser and gets rewarded for the agreed activity conducted by a referred visitor. If publisher "A" attracts publishers "B" and "C" to sign up for the same program using his sign-up code, all future activities performed by publishers "B" and "C" will result in additional commission (at a lower rate) for publisher "A".
In corporate law and taxes, an affiliate is a company that is related to another company, usually by being in the position of a member or a subordinate role, a subsidiary. According to Investopedia, a subsidiary is a company "whose parent is a majority shareholder." (That means the parent owns 51 percent or more of the other company's shares of stock.