A Pingback is one of three types of Linkbacks, methods for Web authors to request notification when somebody links to one of their documents.
https://en.wikipedia.org/wiki/Pingback
Syndication Techniques
Get access to data on 35,479,969 websites that are Pingback Support Customers. We know of 13,616,104 live websites using Pingback Support and an additional 21,863,865 sites that used Pingback Support historically and 1,556,016 websites in the United States.
Get a list of 35,479,969 websites using Pingback Support which includes location information, hosting data, contact details, 13,616,104 currently live websites and an additional 1,145,557 domains that redirect to sites in this list. 21,863,865 sites that used this technology previouslyand 1,556,016 websites in the United States currently using Pingback Support.
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