(1) Deviation of form from normal; specifically, an alteration in shape and/or structure of an organ or other body part; etiology may be developmental, posttraumatic, hereditary, or postsurgical, or due to pathologic conditions in adjacent structures (e.g., compression by a tumor mass). (2) In rheology, the change in the physical shape of a mass by applied stress. [L. de-formo, pp. -atus, to deform, fr. forma, form]