I've heard people use the name "elevator pitch" for a concise answer to a question like "What do you do?" or "What is this company that you run?". I don't think that's a good use of the term. You pitch a specific project or idea (which might be "hire me" but might not.) Answering a small-talk question isn't making a pitch. It does, however, have a lot in common with the elevator pitch - most importantly that you don't have very long at all. Hi, how are you, that's a cool shirt, where do you work, what do you do there - these aren't essay questions.
So you want a concise answer, so that at least you don't talk people's ear off and bore them. And it would be neat if your answer either led the conversation in a direction you'll enjoy, or brought you business, or both. Steve Pavlina has given this quite a bit of thought. It's a long blog post that leads down to 2 or 3 10-12 word sentences, but that's the thing with short statements - they take forever to write.
I've been working on this for a while with gregcons - what's our 10 word answer to what do we do? Generally I say "We solve people's problems. Sometimes we write them software, other times we give them advice on software deveopment or mentor them." If the person looks even vaguely interested I might elaborate, but often that's all the answer they needed. The process of finding this short answer for us, and the process ahead of me to continue to shorten it, does give useful insight into what parts of my job and what parts of this business matter the most to me. I highly encourage everyone whose answer is "all kinds of stuff!" to take the time to find the common thread rather than just listing off a whole pile of -ing verbs until the person who asked slips into a coma. For more on the "what is my real underlying business" (as opposed to the skills you happen to ply in support of that business) you might also want to read a year-ending post from Mike Gunderloy that's just as valid at this time of year.