Engineering jargon for "Subject Matter Expert".
I got a pretty large number of upvotes on the three-word post above so I think the term is common in some circles, unheard of in others. Someone should map it somehow.
To your point, maybe there needs to be an HN glossary of terms or something like that.
I think SME is would be less common in the Bay Area. I tend to associate it's usage with older, less computer tech first, companies.
Never used it at small companies so it seems mostly used at larger companies or relatively new.