So what IS pistou, anyway?

Pistou is seriously good stuff. Made in minutes, from very few (and entirely raw) ingredients, it turns a vegetable soup transcendent, transforms pasta from simple to sublime, and, perhaps less conventionally but no less successfully, it works wonders with certain seafood. The problem is, unlike in the case of its far more famous (and near-mystical-when-done-properly) cousin, pesto, there seems to be no clear agreement on what actually constitutes a true pistou.