TL;DR are there any forum posts or similarly accessible writing that clarify different notions of x-risk? If not, does it seem worth writing?
My impression is that prevailing notions of x-risk (i.e. what it means, not specific cause areas) have broadened or shifted over time, but there's a lack of clarity about what notion/definition people are basing arguments on in discourse.
At the same time, discussion of x-risk sometimes seems too narrow. For example, in the most recent 80K podcast with Will MacAskill, they at one point talk about x-risk in terms of literal 100% human annihilation. IMO this is one of the least relevant notions of x-risk, for cause prioritisation purposes. Perhaps there's a bias because literal human extinction is the most concrete/easy to explain/easy to reason about? Nowadays I frame longtermist cause prioritisation more like "what could cause the largest losses to the expected value of the future" than "what could plausibly annihilate humanity".
Bostrom (2002) defined x-risk as "one where an adverse outcome would either annihilate Earth-originating intelligent life or permanently and drastically curtail its potential". There is also a taxonomy in section 3 of the paper. Torres (2019) explains and analyses five different definitions of x-risk, which I think all have some merit.
To be clear I think many people have internalised broader notions of x-risk in their thoughts and arguments, both generally and for specific cause areas. I just think it could use some clarification and a call for people to clarify themselves, e.g. in a forum post.