The geophysical and dynamical criteria introduced in the “Definition of a Planet in the Solar System” adopted by the International Astronomical Union are reviewed. The classification scheme approved by the IAU reflects dynamical and geophysical differences among planets, “dwarf planets” and “small Solar System bodies”. We present, in the form of a decision tree, the set of questions to be considered in order to classify an object as an icy “dwarf planet” (a plutoid). We find that there are 15 very probable plutoids; plus possibly 9 more, which require a reliable estimate of their sizes. Finally, the most relevant physical and dynamical characteristics of the set of icy “dwarf planets” have been reviewed; e.g. the albedo, the lightcurve amplitude, the location in the different dynamical populations, the size distributions, and the discovery rate.