What is Medium?

Manton Reece in a post about Medium wondered:

Is it a blogging tool? Sort of. Is it a social network? Not exactly.

I've found Medium incredibly useful for browsing a community's current thoughts and ideas. For instance, I love browsing the React tag on Medium. It's filled with various posts about build tools, upcoming libraries, and thought pieces that I would never have found via RSS or Twitter.

Regardless of what Medium intends to be, they at least seem to have stumbled upon something interesting with tags (from my perspective). I'm curious to see how Medium continues to evolve.