A persistent vegetative state is a disorder of consciousness in which patients with severe brain damage

Brain damage

"Brain damage" or "brain injury" is the destruction or degeneration of brain cells. Brain injuries occur due to a wide range of internal and external factors...

 are in a state of partial arousal

Arousal

Arousal is a physiological and psychological state of being awake or reactive to stimuli. It involves the activation of the reticular activating system in the brain stem, the autonomic nervous system and the endocrine system, leading to increased heart rate and blood pressure and a condition of...

 rather than true awareness. It is a diagnosis of some uncertainty in that it deals with a syndrome

Syndrome

In medicine and psychology, a syndrome is the association of several clinically recognizable features, signs , symptoms , phenomena or characteristics that often occur together, so that the presence of one or more features alerts the physician to the possible presence of the others...

. After four weeks in a vegetative state (VS), the patient is classified as in a persistent vegetative state. This diagnosis is classified as a permanent vegetative state (PVS) after approximately 1 year of being in a persistent vegetative state.
A wakeful unconscious state that lasts longer than a few weeks is referred to as a persistent vegetative state.
As opposed to brain death

Brain death

Brain death is the irreversible end of all brain activity due to total necrosis of the cerebral neurons following loss of brain oxygenation. It should not be confused with a persistent vegetative state...

, persistent vegetative state (PVS) is not recognized by statute as death

Death

Death is the permanent termination of the biological functions that sustain a living organism. Phenomena which commonly bring about death include old age, predation, malnutrition, disease, and accidents or trauma resulting in terminal injury....

 in any legal system.