The terms mini-Neptune and sub-Neptune are used for planets between Earth and Neptune in size, that have characteristics more like those of Neptune. There is likely some variation in how the term is used, i.e., which characteristics are under discussion. The terms mini-Neptune and super-Earth may be used based simply upon mass, using some chosen threshold. This can reflect a dichotomy evident in current observational data: there are two peaks in the density function of planet-counts-by-mass that both fall between Earth and Neptune mass, and the two terms may be used merely to categorize planets according to which high-density mass-range they fall under: the existence of these two peaks suggests two types of planet formation. In other discussions, such as those of planet constituents, someone might use super-Earth if it is a rocky planet (as is Earth, but larger), and use mini-Neptune if it is an ice giant (as is Neptune, but smaller). Other terms for the latter are gas dwarf, mini gas giant, and transitional planet.