A nucleus that is not spherical. Nuclei that do not have the magic numbers associated with the shell model tend to be deformed and ellipsoidal. In most deformed nuclei the ratio of the long axis to the short axis is about 1.3:1, but there are more extreme deformations in a superdeformed nucleus and a hyperdeformed nucleus. A deformed nucleus can be regarded as an example of a broken symmetry. Such nuclei have characteristic rotational spectra. A proper quantitative description of deformed nuclei requires the unified model of nuclei.