An elliptical galaxy is a galaxy with an ellipsoidal shape. It is one of three galaxy classes described by Edwin Hubble, along with spiral galaxies and lenticular galaxies. The largest galaxies are elliptical. The galaxy classification designations for elliptical galaxies are E0 through E7. The "E numbers" are based on the galaxy's observed ellipticity, i.e., one minus the ratio of the smaller observed dimension to the larger observed dimension. The E number is an integer rounding of ten times this ellipticity. Elliptical galaxies typically have older, low-mass stars, less interstellar gas and dust, and have little star formation. The colloquial phrase red and dead is used to describe them, implying a low star formation rate, and the lack of blueness, which would be a sign of little star formation since recent star formation would have produced some large, hot, thus bluish, short-lived stars that would still be shining.
A very large elliptical galaxy (giant elliptical galaxy) often resides in the center of a galaxy cluster. Many are what is termed a cD galaxy (a galaxy with a large diffuse stellar halo) cited as meaning "central dominant", but originating as a Morgan galaxy classification term: meaning an extremely large D-type galaxy (a lenticular galaxy).
At least one elliptical has been noted to have a disk-like structure within it, with the potential for some obscured star formation within.