Coke is the solid carbonaceous

Carbonaceous

Carbonaceous is the defining attribute of a substance rich in carbon. Particularly, carbonaceous hydrocarbons are very unsaturated, high-molecular-weight hydrocarbons, having an elevated carbon:hydrogen ratio....

 material derived from destructive distillation

Destructive distillation

Destructive distillation is the chemical process involving the decomposition of feedstock by heating to a high temperature; the term generally applies to processing of organic material in the absence of air or in the presence of limited amounts of oxygen or other reagents, catalysts, or solvents,...

 of low-ash, low-sulfur bituminous coal

Bituminous coal

Bituminous coal or black coal is a relatively soft coal containing a tarlike substance called bitumen. It is of higher quality than lignite coal but of poorer quality than Anthracite...

. Cokes from coal

Coal

Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...

 are grey, hard, and porous. While coke can be formed naturally, the commonly used form is man-made.
The Chinese first used coke for heating and cooking no later than the ninth century AD. By the first decades of the eleventh century, Chinese ironworkers in the Yellow River valley began to fuel their furnaces with coke, solving their fuel problem in that tree-sparse region.

In 1603, Hugh Plat

Hugh Plat

-Life:He was baptised at St. James's, Garlickhythe, on 3 May 1552, he was third son of Richard Plat or Platt, a London brewer; his father owned property in St. Pancras, London, bequeathed much of it to the foundation and endowment of a free school and six almshouses at Aldenham, Hertfordshire, and...

 suggested that coal might be charred in a manner analogous to the way charcoal

Charcoal

Charcoal is the dark grey residue consisting of carbon, and any remaining ash, obtained by removing water and other volatile constituents from animal and vegetation substances. Charcoal is usually produced by slow pyrolysis, the heating of wood or other substances in the absence of oxygen...

 is produced from wood.