Every time I start a new job, I find myself trying to figure out how to best answer the question, "So, what do you do?"
Here's my latest, to the average person who asks:
I design software at Microsoft that helps IT professionals manage their day to day IT operations.
It's concise, digestible and answers a few common questions at the same time:
1. Where do you work? (Microsoft)
2. What is your role? (I design software)
3. What do you work on? (software to help manage day to day IT operations)
4. Who is your customer? (IT professionals)
It's sort of a "pick your poison" question - letting the questioner choose what she wants to ask more about next. What's working at Microsoft like? What do you mean by design software? How does your software help? What kind of day to day operations? Or, sometimes, the questioner just nods quietly, at which point I tell her about all the non-computer stuff I'm interested in too. :-)
Depending on the audience, I might vary the answer from time to time. If I'm talking with someone in the software industry, I might replace "I design software" with my role - "I'm a Program Manager". If I'm talking with someone else who works at Microsoft, I'll replace "Microsoft" with my group, name my product and a few of the other products we ship, and elaborate on some of the scenarios our software enables - anticipating their almost certain follow-up questions.
Depending on the job, I've also varied it quite a bit. When I worked for a small startup, I'd say "a small startup called >Name>". And if the role is generally familiar, it's easy to be even more concise: "I'm a firefighter in <City>."
So, out of curiousity, what do you do? If you took the time to read up to this point, it should only take you about half as long to type an answer in the comments. ;-)