Delirium refers to a cognitive disorder that is acute and usually transient characterized by disorientation, confusion, deficits in memory and Language and memory loss. It is likewis e, characterized by a disturbance of consciousness, a change in cognition that develop over a short period of time and confused state caused by specific organic problems.

Moreover, Delirium refers to a temporary state in which individuals experience a clouding of consciousness in which they are unaware of what is happening around them and are unable to focus or pay attention or a disruption of consciousness often caused by exposure to toxins.

Delirium is also called Acute confusional state or ACS. (See Acute confusional state and ACS).
Other /More definition:
delirium refers to the rapid-onset reduced clarity of consciousness and cognition, with confusion, disorientation, and deficits in memory and language.