What is an ice giant?

Answer 1

An ice giant is a sub category of a gas giant. as there name suggests, ice giants are cold large planets, bigger than earth, either with molten ices such ammonia, methane and water ices, or a large celestial ice ball, with some rock inside or not. if solid ice, then they considered to be as terrestials. the two most perfect examples are Neptune and Uranus, where they have no solid surface, just atmosphere, pressurised molten ices, and possible ice/rocky core. even thouh that they are at least four times larger than earth, and at least fourteen times as massive, their gravity is similar to earth, where is Uranus is 0.9, same as Venus, and Neptune is 1.1,

solid giant ice planets do not occur in our solar system, but may occur elsewhere. if a ice giant is in a habitable zone, it can also be referred as an icy ocean planet, where its surface is just liquid or water, and deeper, hot exotic ice forms.

Answer 2

The ice giants are Uranus and Neptune.

Previously they were classified as gas Giants, but since the voyager flypasts it was noted that they has a completely different structure to the other gas giants (Jupiter and Saturn)

Whereas Jupiter and Saturn are composed of mainly hydrogen and helium, Neptune and Uranus are composed of a rocky core surrounded by a "slush puppy" solution of ice and methane.