1. The term acute encephalopathy refers to a rapidly developing (over less than 4 weeks, but usually within hours to a few days) pathobiological process in the brain. This is a preferred term 2. Acute encephalopathy can lead to a clinical presentation of subsyndromal delirium, delirium, or in case of a severely decreased level of consciousness, coma; all representing a change from baseline cognitive status 3. The term delirium refers to a clinical state characterized by a combination of features defined by diagnostic systems such as the DSM-5. Delirium according to the DSM-5 is defined if criterium A-E are fulfilled: A. Disturbance in attention (i.e., reduced ability to direct, focus, sustain, and shift attention) and awareness (reduced orientation to the environment). B. The disturbance develops over a short period of time (usually hours to a few days) represents a change from baseline attention and awareness, and tends to fluctuate in severity during the course of the day. C. An additional disturbance in cognition (e.g., memory deficit, disorientation, language, visuospatial ability, or perception). D. The disturbances in criteria A and C are not explained by another pre-existing, established, or evolving neurocognitive disorder, and do not occur in the context of a severely reduced level of arousal, such as coma. E. There is evidence from the history, physical examination, or laboratory findings that the disturbance is a direct physiologic consequence of another medical condition, substance intoxication or withdrawal (i.e. because of a drug of abuse medication), or exposure to a toxin, or is because of multiple etiologies. This is a preferred term 4. The term coma refers to a clinical state of severely depressed responsiveness defined by diagnostic systems such as the GCS or FOUR score. This is a preferred term 5. The term acute confusional stateshould not be used in addition to the terms delirium and acute encephalopathy 6. The term acute brain dysfunctionshould not be used in addition to the terms delirium and acute encephalopathy 7. The term acute brain failureshould not be used in addition to the terms delirium and acute encephalopathy 8. The term altered mental status is not synonymous with delirium and should not be used