A plutoid (or ice dwarf, a term more common within science) is a Pluto-like dwarf planet, i.e., icy, round, a trans-Neptunian object (orbits beyond Neptune) and a KBO (Kuiper Belt object). In addition to Pluto, the known examples are Eris, Haumea, and Makemake.
A similar term, plutino is defined as "any size or composition", but like Pluto, in a 3:2 orbital resonance with Neptune and a twotino is like a plutino except that its resonance is 2:1. Other than Pluto, they are all small objects. Estimates are there are thousands of plutinos.