There are differences between management and administration, but sometimes we refer to "manager" and "administrators" interchangeably. Strictly speaking, management involves the making of decisions to promote the goals of an entity, while administration involves seeing to it that the management decisions are carried out. Here are a few example to demonstrate the difference:
A manager decides to impose a sales quota on the company's sales force. The administrator is responsible for seeing to it that the quota is met through the maintenance of records.
A manager decides that there will be a "no tolerance" policy for tardiness. It will be up to the administrator to monitor the compliance of the policy through observation or through the review of records.
So, the general idea is that an administrator is not a primary policy or decision-maker, while a manager is. An administrator might make some decisions to implement the manager's policy's and decisions, but his or her authority is limited.