WordPress pingbacks are a form of automated notification system for WordPress, so that whenever you mention another site or blog post, they get alerted to the mention. Both sites need to have pingbacks enabled in order for this to work - but it can be a very effective way of staying abreast of who’s talking about you.
By default, any post that references another blog post somewhere, internally, or externally, will see WordPress notify that original post owner of the pingback, as well as will receive notifications of linked mentions on other blogs.
Also, pingbacks are, by default, rel=nofollow, which means that some search engines will ignore them, while other search engines will ignore the nofollow flag and will pass along SEO “link juice” (value) from one site to another.
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