What does it mean when an x-ray shows airspace disease with concern for infiltrate?

I am not familiar with the term airspace disease. But suggests there is an possible infiltrate in the lung some where. Most often pneumonia or other lung infection. The Dr who ordered it knows why it was done and can best answer your query.

Any of several conditions like pneumonia, heart failure, non-infectious inflammatory conditions, and more. It depends on information you don't mention: where in your lung(s), how extensive, symptoms (like fever, cough, shortness of breath, chest pain), smoking history, blood oxygenation and other lab results, and other health conditions. Not necessarily serious. Discuss with your doctor.