Chronic back pain is one of the most common and costly disorders. An overview shows that chronicity has various definitions, of which purely temporal ones predominate. Back pain is said to be "chronic" if it lasts for a variable number of weeks or months. Our attempt to refine such definitions is based on three previous works: Loeser's multidimensional pain model, the oncological TNM model and the International Classification of Functioning, Disability and Health of WHO (ICF). We suggest an unidirectional process of pain in the back to a complex pain syndrome including other types of pain, various bodily complaints and cognitive as well as emotional impairments, and propose an empirically testable research model.