The term dwarf planet was coined to apply to solar system objects that are like planets but smaller. Planets and dwarf planets are massive enough to settle into a sphere, but a "full/true/official" planet (per IAU) is also massive enough to clear out a lane through which it orbits (a criteria termed clearing the neighborhood). Dwarf planet is a subtype of minor planet, that later which is any solar system object larger than a meteoroid that is not a comet, moon, or "full" planet.
The term dwarf planet was coined for Pluto and similar objects after multiple similar objects became known. The other known examples are Ceres, Haumea, Makemake, and Eris. Other known, but poorly-resolved bodies may fit the description and there may be more as yet unseen.