An open abdomen is usually what surgeons call the result of leaving the patient's abdomen 'open' after abdominal surgery so that pressures don't build up causing your abdominal organs to stop working. The most common problems being addressed by an open abdomen is abdominal compartment syndrome (ACS) and intra-abdominal hypertension (IAH). These are very complex problems that require complex solutions.
Upon return to the intensive care unit, the patient's abdomen will be open but covered, no doubt, by a special covering to protect the internal organs. The surgeon and the clinical team in the ICU may assess the inside of the abdomen each day and after a period of time where he feels that it's safe to close the abdomen, will take steps to do that.