An override is an agreement between an insurer and intermediary (or between an insurer and reinsurer or a retrocessionaire) based on the percent of written (or ceded) premium that will be guaranteed income to the intermediary/insurer/reinsurer.
There is usually a credit offset for other commissions (regular and contingent commissions) paid. This introduces a question of how fees paid by an insured to an intermediary are handled and should be disclosed along with other income, such as contingent commissions.