Basic Service is the basic entity sourced by different provisioning systems and supplied by different content providers. Each basic service belongs to a service class.
Some of the basic services can be directly sold and some can be bundled and sold to the customer. Basic services are defined in Basic Services Setup screen.
For Example:
HBO channel is the basic service and can be within the service class Pay TV. HBO channel can be given to the end user independently and it can also be bundled with other channels.
An e-mail account is a basic service and should be defined in the service class Electronic Mail. An email account cannot be given to the end user independently. It should be bundled with an Internet Service before being offered to the end customer.