Wiktionary
n. A questioning technique based on discovery and development of personal symbols and metaphors of the person questioned.
Wikipedia
Clean Language is a technique that is used especially in psychotherapy and coaching. Clean Language helps clients to discover and develop symbols and metaphors without being influenced by the phrasing of a question.
Clean Language was developed by David Grove in the 1980s as a result of his work on clinical methods for resolving clients' traumatic memories. As James Lawley and Penny Tompkins describe it, "He realized that many clients naturally described their symptoms in metaphor, and found that when he enquired about these using their exact words, their perception of the trauma began to change."
Clean Language also is the basis of symbolic modeling, a stand-alone method and process for psychotherapy and coaching, which was developed by Lawley and Tompkins.