A biomarker is a measurable indicator or signal that can be used to predict, diagnose, or track a physiological condition or disease. Biomarkers are often substances found in blood, urine, or other bodily fluids and tissues that indicate the presence of a particular disease or health condition. They can also include physical signs or symptoms, genetic markers, or changes in cellular processes that signal the onset or progression of a disease. Biomarkers are used by researchers and clinicians to study diseases, develop new treatments, and monitor patients' responses to therapy.