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. It involves immobilizing an antigen or antibody on a plate, then using an enzyme-linked antibody or antigen to bind to the target. A color change occurs due to an enzyme-substrate reaction, allowing the concentration of the target to be measured. ELISA is widely used in diagnostics and research.