ELISA (Enzyme-Linked Immunosorbent Assay) is a biochemical technique used to detect and quantify substances such as proteins, peptides, antibodies, or hormones in a sample. The method involves immobilizing an antigen or antibody onto a plate, followed by the binding of an enzyme-linked antibody or antigen to the target. When a substrate is added, an enzyme-driven reaction produces a measurable color change, indicating the presence and concentration of the target molecule. ELISA is widely used in research and diagnostics due to its sensitivity, specificity, and versatility.