You must have heard about three kinds of imagination: descriptive, creative and challenging. Roos & Victor introduced those three types of imagination in their 1999 EMJ paper “Towards a New Model of Strategy-making as Serious Play“.
When you are dealing with Lego Serious Play facilitation then the typology of imagination was most probably introduced to you as one of the cornerstones of facilitation concepts on how to encourage different participants to become more active in discussions.
The roots of categorizing imagination are much deeper. The historic concepts were well mapped and elaborated by philosophy professor of Boston University Richard Kearney in his book The Wake of Imagination. Toward a Postmodern Culture.
In this book that was published in 1998, prof. Kearney digs into the history of contemporary imagination, starting from the way imagination was conceptualized by Hebraic legends, in Greek myths, in medieval Christian icons and theology, throughout renaissance and romantic era. Finally he concludes with existentialist takes on imagination and concludes with post-modern contemporary classics.
If you are interested in deep analysis of history and typology of imagination then this book is certainly for you.