What is the difference between ICU and CCU in the hospital?

ICU stands for "Intensive Care Unit."  It is a generic term for a unit that provides critical care and monitoring to patients with non-specific disease entities. Some smaller hospitals may have only one critical care unit, that takes all types of sick adult patients, but most hospitals of any size now have specialty critical care units:
CCU: Coronary (or cardiac) Intensive Care Unit that takes patients who have cardiac-related problems (usually non-surgical).
SICU: Surgical Intensive Care Unit that takes seriously ill patients who have had surgery (including heart surgery).
MICU: Medical Intensive Care Unit that cares for seriously ill patients suffering from non-cardiac medical problems.
Larger teaching hospitals might have several other specialty ICUs such as Neonatal, Respiratory, Pediatric, Neuro, etc.