I haven't seen the term "founding engineer" used commonly, but my assumption is that a founding engineer would be a cofounder with equity comparable to the othe

I haven't seen the term "founding engineer" used commonly, but my assumption is that a founding engineer would be a cofounder with equity comparable to the other founders. However, it seems unlikely that someone would place an ad for a cofounder, so you're probably right that it's just an ad for an early hire that's phrased in a misleading way.