This definition of social media is new to me as well, thanks for sharing it. This sort of clarifies a term I really dislike, and which you’ve used: “the algorithm”. It’s always seemed a little murky to me which algorithms it refers to. It’s like saying “don’t eat food with chemicals in it”.

Lemmy does have “an algorithm”, it’s just a relatively simple one based on communities one is subscribed to plus some vote/comment data for the various sort orderings.

Lemmy also absolutely implements a social graph – the data about who has interacted with whom is all stored by the system. It’s not explicitly stored as a graph structure, but then we’re arguing database schemas.

As I understand it, however, you’re saying “social media” arises when the “social graph” data structure is used as an input to “the algorithm”. That seems like a pretty robust definition to me.

One bit of pedantry: user blocks on Lemmy are, by a general definition, a form of social graph, and they do affect what content people see. So Lemmy could technically qualify as social media by the definition I’ve written here. I’m not sure what a more precise definition could be that avoids this technicality.