Something that's ultra vires is done without the proper authority or power. If the CEO of a company sells a lot of the company's assets without consulting the shareholders, that's an ultra vires action.
Ultra vires is one of many Latin phrases for legal terms. It combines ultra, "beyond," and vires, "strength or power." This term comes up most often in business law, when a corporation violates its bylaws or other contracts and acts in an invalid way. In other words, someone representing the business goes "beyond" their "power" and does something they are not have the authority to do.