The polar ice caps are the regions at the North and South Poles that are covered with ice. They exist because sunlight hits those regions at a less direct angle than at other latitudes due to the curvature of the earth and thus the amount of solar energy from the sun per unit of surface area is less than elsewhere.
The term 'polar ice cap' is somewhat of a misnomer because the term 'ice cap' by itself refers more narrowly to bodies of ice that are over land and measure less than 50,000 square kilometers. Larger bodies are referred to as 'ice sheets.'