Liked Remember WordPress' Pingbacks? The W3C wants us to use them across the whole web by Scott Gilbertson
the goal is to standardize a way to link together conversations across the web. A Webmention is a simple way to notify any URL when you link to it from your site. Consider this scenario: Alice publishes a blog post. Bob writes a response to Alice's post and links to it. On the web as it is today the only real way Alice ever knows about Bob's post is if someone tells her or if she sees incoming traffic in her logs.
Webmentions is a framework for connecting these two posts such that, if Alice's site accepts Webmentions, Bob's publishing software can automatically notify Alice's server that her post has been linked to in Bob's post.
Once Alice's site is aware of Bob's post, Alice can decide if she wants to show Bob's post as a comment on her site or link to it from her post – and if she responds with another post, then the conversation can continue.