Complementary and alternative medicine (CAM) is an umbrella term for many diagnostic and therapeutic methods that lie outside orthodox medicine. It's often described by what it is not, rather than by what it is – not taught in medical schools, not scientifically proven, not on the NHS, not plausible, not orthodox.
The Cochrane Collaboration (an international organisation that produces reviews of published evidence of drugs and health interventions) has adopted the definition of CAM as:
"Diagnosis, treatment and/or prevention which complements mainstream medicine by contributing to a common whole, by satisfying a demand not met by orthodoxy or by diversifying the conceptual frameworks of medicine".
It's important to differentiate between therapies that complement orthodox treatment, for instance aromatherapy being used alongside drugs for pain relief, and those sought as an alternative.