What is the definition of an Agent ?

What is the definition of an Agent ?

We are a subscriber for Zoho Mail and is interested in the Zoho Support feature.

May I know what is the definition of an agent ?

In our company we have 1 helpdesk person and 4 technicians. All communication with the customer is done by the helpdesk person. When a support request is received, the helpdesk person need to assign to anyone of the 4 technicians. When the task is done, our technician will email to our helpdesk person on the status.

How many agents subscription do I need ?