ILD (interstitial lung disease) refers to a group of lung conditions that cause scarring (fibrosis) of the lung tissues, leading to difficulty in breathing. This scarring makes the lungs stiff, reducing their ability to expand properly and take in oxygen. ILD can be caused by long-term exposure to harmful substances like asbestos, certain medications, and autoimmune diseases, or it can sometimes occur without a known cause (idiopathic).