What does the term "infiltrate" refer to in radiology?

In radiology, the term "infiltrate" refers specifically to an ill-defined radiodensity seen on imaging studies, particularly in the context of the lungs. An infiltrate generally suggests the presence of abnormal material within the lung parenchyma, such as fluid, pus, cells, or other substances. This term is often used in the diagnosis of conditions like pneumonia, where the lung fields may appear hazy or cloudy rather than clear, indicating the presence of these abnormal substances.

The choice of "any ill-defined radiodensity" captures the concept accurately because infiltrates do not present in a discrete or well-defined manner; instead, they appear as diffuse areas of opacity. Understanding this terminology is crucial for healthcare professionals when interpreting chest X-rays or CT scans, as it informs potential diagnoses and treatment plans.