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 33,851,709 websites that are Pingback Support Customers. We know of 13,616,104 live websites using Pingback Support and an additional 20,235,605 sites that used Pingback Support historically and 1,464,087 websites in the United States.
Get a list of 33,851,709 websites using Pingback Support which includes location information, hosting data, contact details, 13,616,104 currently live websites and an additional 1,124,691 domains that redirect to sites in this list. 20,235,605 sites that used this technology previouslyand 1,464,087 websites in the United States currently using Pingback Support.
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