@joelars – Good morning. I'm sorry to hear that you have been ill. I had pneumonia a couple of years ago and it wasn't fun. I am a 22+ year lung cancer survivor with COPD and Emphysema. @ethanmcconkey is correct in his definition of perihilia infiltrate. The denser than air is a fancy schmancy term for pus, protein, or blood. They are very common and associated with pneumonia and a couple of other lung illnesses. I imagine that the medicines that you were sent home with will help get rid of them and that you will be feeling much better sooner than later.