Announcement reposted from Amazon:
Starting October 6, product listings for certain categories including health and personal care, home, and sports, will display a “sales trend” that highlights how many customers recently purchased that product.
“Sales trend” is a new listing feature that provides a broad estimate of the number of customers who recently bought a particular product. For example, the listing might show “10K+ bought in past month.” The feature is designed to help customers find your most recent popular products.
Similar to customer reviews, badges, and sales rank, sales trend is automatically added to eligible listings.
To find out more, go to Sales trend FAQ.