This song is about an unemployed steelworker in Youngstown, Ohio. Most people think that Bruce is singing this song to a woman named Jenny ("my sweet Jenny I'm sinkin' down" etc.), but "Jenny" is the nickname given to the Blast Furnace at Youngstown steelworks - The Jeanette Blast Furnace (named after the daughter of W.A. Thomas, who was the President of Brier Hill Steel).
It's common practice at steelworks to have nicknames for blast furnaces - for example, at Scunthorpe steelworks in the UK the four furnaces are known as Bess, Victoria, Anne and Mary (after four Queens of England/Britain). The fact that Bruce's character is singing to the furnace, rather than a person, changes the song considerably.