According to the World Health Organization (WHO), a medical error is defined as a preventable adverse effect of medical care, whether or not it is evident or harmful to the patient. This includes errors in diagnosis, treatment, medication, equipment, or systems failure in healthcare delivery.

The WHO emphasizes that medical errors can occur at any point in the healthcare process, from diagnosis to treatment to post-treatment care. These errors can result from various factors, such as communication breakdowns, misinterpretation of information, technical failures, inadequate healthcare systems, or human error.

It is important to note that medical errors are not intentional actions, but rather unintended mistakes or failures that occur during the provision of healthcare services. The WHO emphasizes the need to identify and learn from these errors to improve patient safety and the quality of healthcare delivery.