The basic difference between coal and coke is that coal is the natural source and coke is the derivative product produced by destructive distillation. Both are used as fuel, but coke contains a higher carbon content and few impurities. Coke is also used during iron ore smelting as a reducing agent.
Coal is a naturally-found fossil fuel that is formed by the anaerobic decay of plant life taking place over millions of years. The energy released when the fuel is burned comes from the initial solar energy that remains stored in the hydrocarbons contained in coal. Coke is what remains when the impurities in coal, such as coal-tar and coal-gas, are removed by high temperatures in an oxygen-free furnace. The absence of oxygen during the process prevents the coal from burning. Unlike coal, coke can be burned with little or no smoke.