Decentralization is the tendency to disperse decision-making authority in an organization structure. To the extent authority is not delegated, it is centralized.
There could be absolute centralization of authority in one person. But that implies no subordinate managers and, therefore, no structured organization. Some decentralization exists in all organizations. On the other hand, there cannot be absolute decentralization, for if managers should delegate all their authority, their status as a manager would cease, their position would be eliminated and there would, again, be no organization. In other words, no organization can be completely centralized or decentralized.