Webmention is a web standard for mentions and conversations across the web, a powerful building block that is used for a growing federated network of comments, likes, reposts, and other rich interactions across the decentralized social web.
”… an @ mention that works across websites; so that you don't feel immovable from Twitter or Fb.” — Rony Ngala
When you link to a website, you can send it a Webmention to notify it. If it supports Webmentions, then that website may display your post as a comment, like, or other response, and presto, you’re having a conversation from one site to another!
https://indieweb.org/Webmention