what is mean by I C U

An intensive care unit (ICU), also known as a critical care unit (CCU), intensive therapy unit or intensive treatment unit (ITU) is a special department of a hospital or health care facility that provides intensive care medicine.

Intensive Care Units cater to patients with the most severe and life-threatening  illnesses and injuries; that require constant, close monitoring and support from specialist equipment and medication in order to maintain normal body functions. They are staffed by highly trained doctors and critical care nurses who specialize in caring for seriously ill patients.