A Tariff (for Tenant billing purposes) is linked to a single Tenant Provider Contract and defines the set of charges that will be calculated during the production of Tenant Bills.
The Cost Definition is associated to the Tariff and holds details of the unit rates that should be used for specific periods of time. For example the Cost Definition can hold the Pence Per Unit you want to charge and any apportionment by time of day (e.g. day/night rates). Cost Definitions will need to be set up first so that it can then be associated with the Tariff.