Noun
(astronomy) An icy planetoid: an astronomical object, such as Pluto, Sedna or (for some authors) Ceres that is large enough to be a world and contains more ice than a typical asteroid.
(astronomy) A centaur or transneptunian object.
(astronomy) An astronomical object that is larger than the core of a typical comet and icier than a typical asteroid.
Source: en.wiktionary.org