The difference at a glance
The terms are often used interchangeably, but they describe different levels of ambition. A helpdesk exists to solve problems: someone reports, someone fixes. The focus is fast resolution, ticket by ticket.
A service desk takes a holistic view. It is a contact point for all IT services and connects to the processes that govern delivery – incidents, requests, changes and self-service. The helpdesk handles the symptoms; the service desk handles the entire service delivery.