Oblate spheroid

From Tardis Wiki, the free Doctor Who reference

An oblate spheroid was a geometric shape the the Fourth Doctor used to describe the planet Calufrax. (DW: The Pirate Planet)

The Doctor never actually explains what an oblate spheroid is. However, the model for the miniaturized Calufrax does conform roughly to the shape of a real-life oblate spheroid.
Oblate spheroid