California Code, Business and Professions Code - BPC § 22590

As used in this chapter, a “hosting platform” means a marketplace that is created for the primary purpose of facilitating the rental of a residential unit offered for occupancy for tourist or transient use for compensation to the offeror of that unit, and the operator of the hosting platform derives revenues, including booking fees or advertising revenues, from providing or maintaining that marketplace. “Facilitating” includes, but is not limited to, the act of allowing the offeror of the residential unit to offer or advertise the residential unit on the Internet Web site provided or maintained by the operator.