Depends on who is asking. 

I, like most everyone get asked on a regular basis what I do for a living. It’s not really complicated (don’t tell anyone) but I find myself inevitably describing it differently based on who I am talking to. Not sure why. Feel free to email me with a diagnosis of my particular brand of neurosis.
 
The standard elevator pitch:
Invention and Intervention of early stage companies. I conceptualize market solutions to problems and partner with entrepreneurs to prove viable and iterate them scalable. I also get asked to intervene, typically on the behalf of investors in companies that are having trouble successfully reaching their market. I work closely with them to pivot their model and package it so that potential customers can better understand and interact with them.

To an ambitious, budding entrepreneur:
I make quick, cheap mistakes and measure them closely towards not repeating them. I save you from making long, expensive mistakes that typically kill ventures before they ever get traction.

To an early stage investor:
I hedge your risk with a no bs approach to testing viability and minimize burn rate with efficient operational models and measurable marketing campaigns.

To my grandmother:
I build cool stuff on the Internet Nan.

To a big corporation:
I show you and help you implement what two kids are currently building in a Starbucks somewhere that will serve to suck the profit out of your margins over the next few years until you eventually cease to exist.

To the girl in a loud bar after a few drinks:
Have you ever seen The Social Network?

To myself when I am exhausted:
What are you doing? Wait. Are you kidding? I love this stuff. Get some sleep.