Lemmy, PieFed, and mbin/kbin all provide APIs that let you pull data (communities, posts, users) from their backend. A client knows how to connect to the API, pull the data, and present it to the user. Lemmy, PieFed, and mbin all have a default client they ship with, but the Lemmy client only speaks Lemmy, the PieFed client only speaks piefed, etc.

Blorp, among other multi platform clients, speaks Lemmy and PieFed. Blorp can be self hosted, but it’s not a backend like Lemmy, PieFed, etc. Blorp reads/writes data via these APIs, but it doesn’t store any data on a server.

Idk if I explained that well. Does that make any sense?

Other way to think about it is email. Gmail is both a email server and a client. Blorp is like using a 3rd party email client that connects to Gmail and Yahoo.