Roasting is cooking with dry heat, whether an open flame, oven, or other heat source. Roasting usually causes caramelization of the surface of the food, which is considered a flavor enhancement. Meats and most root and bulb vegetables can be roasted.
The only difference between baking and roasting is that baking excludes open flame. Wikibooks Wikibooks Cookbook has more about this subject: Roasting
There is a second definition of roasting that has become popular in the UK in recent years, which refers to sex act committed by several men and one woman. It is said to be popular with premiership footballers.