A biomarker is a measurable indicator of a biological condition or process. It can be a substance, such as a protein or gene, found in blood, tissues, or other bodily fluids. Biomarkers are often used in medicine to diagnose diseases, monitor health conditions, or assess responses to treatments. In research, biomarkers help scientists understand disease mechanisms and develop new therapies. For example, cancer biomarkers can indicate the presence of tumors or predict how well a patient might respond to a specific treatment. Overall, biomarkers play a crucial role in personalized medicine and improving patient care.