Marketing engineering happens when the person you bring in isn't limited to one lane. Not a developer who only writes code. Not a strategist who only writes decks. Not a marketing-ops person who only lives inside HubSpot. Not an integrator who only wires tools together.
Someone who does all of it, in the mix required, to produce something that runs.
The term is having a moment for a reason. Marketing teams have more tools than ever, more data than ever, and more surface area than ever. But the person who can span all of it and deliver a working outcome is still rare. Most in-house marketing engineers work at big companies. Most tool vendors are building product, not custom solutions. Most agencies stop at the edges of the platforms they specialize in.
The slot that stays mostly empty is the fractional operator who spans it all. That's the slot I work in.