The seller-paid commission offered to the buyer’s agent. The commission is technically paid to the real estate firm where the agent works, and that firm then splits the commission in some fashion with the agent. That split can be a percentage, or simply paid via a flat monthly fee (a "desk fee").
Most people assume that the split is even (so the typical 3% is split evenly between the firm and the agent). But that is rarely the case anymore. The "splits" vary from office to office and within offices, based on an agent's "production." The more commissions they earn, the better their splits will likely be.