agent

1. A program that performs a task in the background and informs the user when the task reaches a certain milestone or is complete.
2. A program that searches through archives looking for information specified by the user. A good example is a spider that searches Usenet articles. Sometimes called an intelligent agent.
3. In SNMP (Simple Network Management Protocol), a program that monitors network traffic.
4. In client-server applications, a program that mediates between the client and the server.