An ELISA (Enzyme-Linked Immunosorbent Assay) test is a serology test used to detect and measure antibodies, antigens, proteins, and hormones in bodily fluids like blood. It's a common laboratory technique used to diagnose various conditions, from infections to hormone imbalances. The test relies on enzymes linked to antibodies to detect specific molecules in a sample, often by color change, which indicates the presence and sometimes the quantity of the target substance.