Coal is an aesthetic surrounding coal and it's industrial usage in coal power stations, trains, steel, etc... This aesthetic has a dark and negative feel to it, mainly surrounding the pollution and the loss of jobs regarding the fact that coal is increasingly used less and the impact that it has on multiple communities that heavily rely on coal, both in the United States and worldwide in general.
The fashion of coal is usually industrial working clothing (Boiler suits, overalls, shirts, helmets) mainly used for mining and processing coal or using it in other industrial circumstances, as usually, fancy and formal clothing isn't suited to the harsh working conditions of this industry
While there are varieties of music related to the Coal aesthetic, ones that stick out are songs sung by coal miners about the hard working conditions in mines of various time periods, particularly the 19th century, as that is when the coal industry had it's biggest boom. These songs typically talk about hardships and oppression from their bosses, or just simple things in life such as minecarts and their homes.