A service is a broadly-defined area of work effort that we do for a customer rather than their doing it themselves. It might be preferable that we do it due to efficiency, desire for centralization, quality, reduced risk, or that the customer doesn't want to expend effort developing the expertise independently.

A service offering is more specific component of delivery of the service. For example, the Audio and Video service includes the service offerings web conferencing, event technical support, and digital signage.