In larger corporations and institutions you will sometimes see that the holder of an office is also deemed to be a member of the board of directors or the board of trustees “ex officio.”
The term ex officio means “by virtue of one’s office,” and the designation is typically used to indicate that an officer of a company or other institution, such as the president, is also automatically a member of the board of directors or possibly certain committees of the entity. The purpose is to insure that the person responsible for day-to-day management of the entity is also involved in the long-term planning and management, which is usually conducted at the board of director level.
– BBC&B