What I do: I write the software that lets other software developers get their job done; and in a circular way, I use the software I write to write the same software. If someone is technical, I can explain that I work on compilers.

But when I want to explain to non-techies what it actually entails: I say I sit in front of a text editor which contains precise instructions telling the computer what to do; and I edit it, slowly and experimentally, trying to get it right. It's almost like a poetry epic: low-level rhythm and rhyme, but high-level story.