I think he's talking about Lending, as in the ability to lend a book to another person for 2-weeks, one-time-only, etc.
http://www.amazon.com/gp/help/custom...deId=200549320
There is also the Kindle Lending Library for Prime members.
I think there are some UK restrictions on both, though...?
(ETA: If it is available, do what DiapDealer said.

)