A sled, skid, sledge, or sleigh is a land vehicle that slides across a surface, usually of ice or snow. Various types of sleds are pulled by animals such as reindeer, horses, mules, oxen, or dogs. Sleds are especially useful in winter but can also be drawn over wet fields, muddy roads, and even hard ground if one helps them along by greasing the blades ("grease the skids") with oil or alternatively wetting them with water.

Source: Wikipedia