Too many people are confusing the two. Whenever lemmy.ml or its devs do something stupid, people go “Lemmy is getting worse and worse,” or “I’m leaving Lemmy,” or worse, “I’m leaving for Beehaw.”
If you’re using Beehaw, then you’re using Lemmy. Lemmy is the software these instances run on. If you don’t like lemmy.ml, join another instances that have rules that match your philosophy. Some instance hosts authoritarian or fascist shit? Turn to another Lemmy instance. Lemmy.ml is not even the biggest instance. People who just joined and are unfamiliar with the platform will just think the entire Lemmyverse is run by autocratic admins if we don’t get our terminology right.
I don’t think there is a clear and consistent answer to this question. Like asking a conservative what “woke” means, it is used to refer disparagingly to a wide variety of people that a given person doesn’t like.
I’m pretty far left myself in my way of thinking, and I don’t support some people that I would agree adhere to the description of tankie. There’s a clear definition, even if it is used in a derogatory way. It’s someone who thinks that left ideas should be spread in an authoritarian way. Which, in my opinion, is pretty much the definition of fascism. Power for power’s sake, domination just to say they won. Authoritarian imposition of ideology is antithetical to socialism.
Every person that I’ve seen describe it says some variation of “they’re fake marxists that support anything that opposes the west, include fascist and violent regimes.” Conservatives use “woke” to refer to anything that opposes christofascist white supremacy, from gay pride parades to a black person appearing in a movie.
There are liberals who use “tankie” to refer to anyone left of socialdemocracy, but not a single time have I seen the term being used that way to define another user on any lemmy instance yet.