Often it's easier to define impro by what it isn't. It isn't scripted theatre and it isn't stand-up comedy. It isn't pantomime and it isn't avant garde socio-political monologue. But it does combine elements from all of those.
|Jochem Meijer as Yeus, God of Improv by Rick vd Meiden
When telling an audience what it is, I say it's "the noble art of making stuff up on stage." But to a more scientific audience, such as yourselves, I would say it is "a form of comedy theatre using simple techniques to create new scenes based on little or no initial information." And now it doesn't sound fun at all. So let's get a bit more artsy, "a system of theatre using listening and positive play techniques to build scenes and stories using a combined imagination." But quite frankly, once you are an advanced improviser, who has absorbed so many of the general improv guidelines and for whom the core rules of listening and agreeing are habitual, you could describe it as "dicking around on stage." The problem is that for a tight group of advanced improvisers, dicking around on stage is like watching wonderful theatre. Lesser performers can't just dick around on stage because it just looks like dicking around on stage, and nobody wants to watch that for an hour unless you already really, really like the performers.
So if I had to give one definition out of all of these it could be "The noble art of dicking about on stage to build stories through simple listening and positive play techniques" But I'd like to go with something simpler, that I'm sure has been used before:
Stories from a collective imagination.