The French term ‘terrain vague’ experienced an astonishing career in different languages since the end of the twentieth century although it entails many problems of definition and translation. Taking this double difficulty as a starting point, this study investigates the precise systematic position and function of the term by relating it to other key concepts of spatial theories, such as ‘zone blanche’, ‘non-lieu’ and ‘hétérotopie’, and by tracing its literary history from the Romantic period to present times. Within this framework the essay tries to elucidate the fact that since Hugo and Balzac one can distinguish between two poetically and aesthetically different kinds of employing the concept of ‘terrain vague’. Thus, it is presented as a model of social utopia, often incarnated by children at play, or as an intimidating place inhabited by people inclined towards transgression.