A polar ice cap is a high latitude region of a planet

Planet

A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...

 or natural satellite

Natural satellite

A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its primary. The two terms are used synonymously for non-artificial satellites of planets, of dwarf planets, and of minor planets....

 that is covered in ice

Ice

Ice is water frozen into the solid state. Usually ice is the phase known as ice Ih, which is the most abundant of the varying solid phases on the Earth's surface. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions...

. There are no requirements with respect to size or composition for a body of ice to be termed a polar ice cap, nor any geological requirement for it to be over land; only that it must be a body of solid phase matter in the polar region

Polar region

Earth's polar regions are the areas of the globe surrounding the poles also known as frigid zones. The North Pole and South Pole being the centers, these regions are dominated by the polar ice caps, resting respectively on the Arctic Ocean and the continent of Antarctica...

. This causes the term 'polar ice cap' to be something of a misnomer, as the term ice cap

Ice cap

An ice cap is an ice mass that covers less than 50 000 km² of land area . Masses of ice covering more than 50 000 km² are termed an ice sheet....

 itself is applied with greater scrutiny as such bodies must be found over land, and possess a surface area of less than 50,000 km²: larger bodies are referred to as ice sheets.

The composition of the ice will vary.