1. A nonhereditary change in an organism; e.g., one that is acquired from its own activity or environment.
2. A chemical or structural alteration in a molecule.
behaviour modification, the systematic use of principles of conditioning and learning, especially operant or instrumental conditioning, to teach certain skills or to extinguish undesirable behaviours, attitudes, or phobias.
chemical modification, alteration in the structure of a molecule, typically a macromolecule such as a protein, by chemical means; often, the covalent addition by some reagent.
covalent modification, alteration in the structure of a macromolecule by enzymatic means, resulting in a change in the properties of that macromolecule; frequently, this type of modification is physiologically relevant.