My friend Rob has just written a post about trying to describe his field. He distinguishes between the casual “so what are you studying” and true interest in your research field. The difference between the conversation-halting, “Parallel scalability for algebraic multigrid methods applied to symmetric positive definite systems that arise from computational biological problems,” and the better-thought out

Abstracting further, [the products of] my field can solve differential equations, which means that it can solve most equations produced by physics. The solutions produced by these calculators describe how the world works. When ever you see a weather forecast, you’re seeing the output of these types of these advanced calculators.

is vast. This goes along with something I discussed with Amanda the other day. It doesn’t matter what field you’re writing for – the message should never be hidden behind words. He actually gives several levels of abstraction, a useful set of responses for tailoring your response to your audience.