Amazon defines "WW paid units -- Y/Y growth" as:
Physical and digital units sold (net of returns and cancellations) by us and sellers in our stores as well as Amazon-owned items sold in other stores. Units sold are paid units and do not include units associated with AWS, certain acquisitions, certain subscriptions, rental businesses, or advertising businesses, or Amazon gift cards.
Last reported quarter 2021 Q1 it was 44.0%, up by 38% year-over-year from 32.0%.
Source: Amazon Quarterly Results.