"A two-part tariff (TPT) is a price discrimination technique in which the price of a product or service is composed of two parts - a lump-sum fee as well as a per-unit charge. In general, price discrimination techniques only occur in partially or fully monopolistic markets." - this is from Google search for "two-part tariff"

https://en.wikipedia.org/wiki/Two-part_tariff

http://lexicon.ft.com/Term?term=two_part-pricing