Terminology around the motor neurone diseases can be confusing; in the UK "motor neurone disease" refers to both ALS specifically (the most common form of disease) and to the broader spectrum of motor neurone diseases including progressive muscular atrophy, primary lateral sclerosis, and progressive bulbar palsy. In the United States the most common terms used are ALS (both specifically for ALS and as a blanket term) or "Lou Gehrig's disease".

Amyotrophic comes from the Greek language: A- means "no", myo refers to "muscle", and trophic means "nourishment"; amyotrophic therefore means "no muscle nourishment," which describes the characteristicatrophication of the sufferer's disused muscle tissue. Lateral identifies the areas in a person's spinal cord where portions of the nerve cells that are affected are located. As this area degenerates it leads to scarring or hardening ("sclerosis") in the region.