An employee or agent of a company has apparent authority to transact on behalf of the company if his function or standing with the company will lead a reasonable person to believe that the company person has authority to transact, whether or not s/he actually has that authority.
For instance, if a company made someone VP of Purchasing, one would reasonably believe that this person can purchase on behalf of the company. More to the point, if a Manager of Purchasing had the authority to purchase up to $1 million, and actually made a purchase of $2 million, in most cases the manager would have "apparent" (though not actual) authority to make the $2 million purchase.
If one is a member of the company's Board of Directors, the term "ostensible authority" is used to describe apparent authority. How does this work, and does it differ in any way from "apparent authority." Put another way, what gives (or removes) "ostensible authority" from a board member to deal on behalf of the company.