ELISA (Enzyme-Linked Immunosorbent Assay) is a biochemical technique used mainly in immunology to detect the presence of an antibody or antigen in a sample. This technique is based on the specific binding between an antigen and an antibody, which allows for highly specific detection of substances. In ELISA, enzymes linked to antibodies produce a detectable signal, usually colorimetric, which indicates the presence of the target molecule.