You shouldn't have to click away from a blog post to understand what the blog post is about. It should start with a clear self-contained introduction.

atproto.com contains a succinct discription:

> Atproto is a big-world open social protocol. Users publish JSON records into repositories. The changestreams of those records then sync across the network to drive applications.

Still a bit abstract, but OK. Personally I would include that AT protocol stands for Authenticated Transfer Protocol and that it is the protocol powering Bluesky.