According to Baines (2007), PSS is a market proposition that extends the traditional functionality of a product by incorporating additional services, where the focus is “sale of use” (the customer pays for using an asset, rather than its purchase). 

Tukker (2015) distinguishes three types of PSS: product-oriented PSS (products are sold to the user, but additional services are added, such as maintenance); use-oriented PSS (the business model is geared toward selling the product function, that is, through leasing or renting and the product remains the ownership of the PSS provider); and result-oriented PSS (the business model is geared toward selling a result and is as such closest to offering a pure service, where no predetermined product is involved).

BAINES, T. S. et al. State-of-the-art in product-service systems. Journal of engineering manufacture, 221(10), 1543-1552, 2007.

TUKKER, A. Product services for a resource-efficient and circular economy–a review. Journal of cleaner production, 97, 76-91, 2015.