A tariff is effectively a way to label a company-specific pricing structure, which can be applied to a product, service or rate sheet.
The usage of tariffs varies from company to company, but the easiest way to explain them would be to imagine you have two tariffs called Retail and Wholesale. Products, services or rates associated to the Retail tariff, for example, would feature higher prices than those of their Wholesale counterparts.
By default, Billingbooth has a Standard tariff set up for you already.
Billingbooth will use the default tariff's pricing structure if no others are available.
For example, let's say you have your Standard tariff set to default and you also have a Premium tariff. You bill a Premium customer for an ACME Handset which has a price applied to the Standard tariff but no price applied to the Premium tariff, Billingbooth will resort to using the default Standard tariff and therefore charge your Premium customer the Standard tariff amount for the ACME Handset.