The ice sprites are a race of humanoids who inhabit the Land of Snow, a plane different from Gielinor. The only known members of this race are the Queen of Snow and her sister, the Ice Queen. Additionally Jack Frost is half ice sprite, being the son of the Queen of Snow.
Ice sprites seem to generally have pale blue skin and blue hair, and possess certain powers over cold and water. Jack Frost can be seen displaying these powers during the 2008 Christmas Event, and the Queen herself is charged with bringing snow to RuneScape during Christmas time.
Ice sprites age extremely slowly by human standards. Jack Frost is 44 years old in human years, but has the physical and mental age of a seventeen-year-old boy. As he is also half human, this would imply that Ice Sprites age more than 4 times slower than humans.