煤气从字面意思上讲是与煤有关的气体，但是在不同的使用环境下，煤气具有不同的解释：

Coal gas is a flammable gaseous fuel made from coal and supplied to the user via a piped distribution system. Town gas is a more general term referring to manufactured gaseous fuels produced for sale to consumers and municipalities.

Coal gas contains a variety of calorific gases including hydrogen, carbon monoxide, methane and volatile hydrocarbons together with small quantities of non-calorific gases such as carbon dioxide and nitrogen.