The act or an instance of transforming: her difficult transformation of the yard into a garden. The state of being transformed: impressed by the transformation of the yard. A marked change, as in appearance or character, usually for the better: recent transformations in the format of the publication. Mathematics Replacement of the variables in an algebraic expression by their values in terms of another set of variables. A mapping of one space onto another or onto itself. Linguistics An operation or rule that changes one linguistic structure (especially a syntactic structure) into another, as by the merger, relocation, or deletion of one of its constituents. Genetics The change undergone by an animal cell upon infection by a cancer-causing virus. The introduction of DNA from one cell into another by means of a bacteriophage or one of a variety of chemical or physical methods.