Natural Gas (NG) (Wikipedia) is composed primarily of Methane which is itself a Greenhouse Gas and a Fossil Fuel. (A strong-smelling "stenching agent" may be added to supplies to alert people to leaks by producing a distinctive smell.) When burned NG produces significantly less CO2 than coal. It is also relatively easily transported, though pipelines, compressed in tanks for transport applications (e.g. buses) or liquefied for bulk transport of NG supplies.
Natural Gas is found in underground reserves which may be exploited by conventional drilling. Increasingly it is accessed by Fracking.
Proposals to Eliminate Natural Gas from the Fuel Mix Are Premature Andrew Campbell; Berkeley Haas; 17 Oct 2016