These include:

Epidemic neuromyasthenia was a term used for outbreaks with symptoms resembling poliomyelitis. Iceland disease and Akureyri disease were synonymous terms used for an outbreak of fatigue symptoms in Iceland. Low natural killer syndrome, a term used mainly in Japan, reflected research showing diminished in vitro activity of natural killer cells isolated from patients. Neurasthenia has been proposed as an historical diagnosis that occupied a similar medical and cultural space to CFS. Royal Free disease was named after the historically significant outbreak in 1955 at the Royal Free Hospital used as an informal synonym for "benign myalgic encephalomyelitis". Tapanui flu was a term commonly used in New Zealand, deriving from the name of a town, Tapanui, where numerous people had the syndrome. Society and culture
Naming
Many names have been proposed for the illness. Currently, the most commonly used are "chronic fatigue syndrome", "myalgic encephalomyelitis", and the umbrella term "ME/CFS". Reaching consensus on a name is challenging because the cause and pathology remain unknown. : 29–30 The term "chronic fatigue syndrome" has been criticized by some patients as being both stigmatizing and trivializing, and which in turn prevents the illness from being seen as a serious health problem that deserves appropriate research.
A two-day CPET cannot be used to rule out chronic fatigue syndrome. : 216

Definitions
Notable definitions include:
Centers for Disease Control and Prevention (CDC) definition (1994), the most widely used clinical and research description of CFS, is also called the Fukuda definition and is a revision of the Holmes or CDC 1988 scoring system. The 1994 criteria require the presence of four or more symptoms beyond fatigue, while the 1988 criteria require six to eight. The ME/CFS 2003 Canadian Clinical working definition states: "A patient with ME/CFS will meet the criteria for fatigue, post-exertional malaise and/or fatigue, sleep dysfunction, and pain; have two or more neurological/cognitive manifestations and one or more symptoms from two of the categories of autonomic, neuroendocrine, and immune manifestations; and the illness persists for at least 6 months". The Myalgic Encephalomyelitis International Consensus Criteria (ICC) published in 2011 is based on the Canadian working definition  and has an accompanying primer for clinicians The ICC does not have a six months waiting time for diagnosis. The ICC requires post-exertional neuroimmune exhaustion (PENE) which has similarities with post-exertional malaise, plus at least three neurological symptoms, at least one immune or gastrointestinal or genitourinary symptom, and at least one energy metabolism or ion transportation symptom. Unrefreshing sleep or sleep dysfunction, headaches or other pain, and problems with thinking or memory, and sensory or movement symptoms are all required under the neurological symptoms criterion. According to the ICC, patients with post-exertional neuroimmune exhaustion but only partially meet the criteria should be given the diagnosis of atypical myalgic encephalomyelitis.