POSSE is an abbreviation for Publish (on your) Own Site, Syndicate Elsewhere, a content publishing model that starts with posting content on your own domain first, then syndicating out copies to 3rd party services with permashortlinks back to the original on your site.
POSSE lets your friends keep using whatever they use to read your stuff (e.g. silo aggregators like Facebook, Tumblr, Twitter, etc.).
I like having my own content on my own site, even in cases where I first publish it elsewhere. I believe that my blog should have, if not everything, at least most of what I publish around.
That's why I put together some IFTTT (If This Then That) recipes, that keep an eye on my blog's feed and when a new post is published, they automatically share it on Facebook, Twitter and Medium.
And, if everything went well, you should see this post there too :-)