AAP is the Amazon Advertising Platform, a DSP from Amazon, where advertisers and trading desks can buy advertising programmatically.
AAP DSP has exclusive inventory, the possibility to track sales on Amazon, and specific audiences from Amazon users. This is what makes Amazon a valuable DSP on the market.
Amazon DSP has ad exclusive ad types. See here the ads:
On the publisher side, Amazon has an header bidding solution, so it is integrated directly with many publishers.
Here is the link to access the AAP DSP.