ELISA, or enzyme-linked immunosorbent assay, is a commonly used biochemical technique for detecting the presence of specific proteins, antibodies, or antigens in samples. It involves using antibodies linked to enzymes to detect the target molecule, which produces a measurable signal that indicates the presence and quantity of the molecule in the sample. ELISA is widely used in research, diagnostics, and drug development, and is a sensitive and efficient tool for detecting a wide range of proteins and other molecules in biological samples.