Former head of engineering at Pinterest here. Marty was one of the first three engineers at the company. He is an amazing guy -- smart, personable, fun to work with.

This is a boon for Reddit and as a Reddit user I'm very excited. Fortunately Pinterest has a strong bench and can afford to share the wealth of their amazing engineering team.

Basically "Engineer hire #1" (or similar) that was on board super early but wasn't part of the founding team when the team itself was formed.

I am guessing the distinction is to delineate the fact that the engineer did not join 1+ year from company founding, which is often the case for Engineer #1.

So basically founder minus the shares?

Well in the case I saw it was founder minus the shares plus quite good pay.

and not promoted to direng/cto or (s)he would have use that title, though maybe the company has a policy of not promoting interally

Same way the Mercury Seven were "founding astronauts": the first class, the inaugural group, etc.

likely first or second employee that joined the company

Ok, since "founding" is misleading (or at least distracting) we've replaced it with "early" above.

Interesting, since the TechCrunch article uses the phrase 'Founding' Engineer

The HN guidelines ask submitters to use the original title unless it is misleading or linkbait. In the latter cases it's standard practice for us to change them here. I don't really think the Techcrunch title was misleading, and you were certainly right to post it as is. But the word "founding" did spark an off-topic subthread, and in cases like that we've found it's easiest to just remove the objection.