Coal-seam is a term used to describe a layer of coal that is found underground. It is usually formed from the remains of ancient plants and is mined for its energy content. The crossword solutions for this term are 'VEIN' and 'WELT'. A VEIN is a narrow, elongated deposit of mineral ore or coal, while a WELT is a raised ridge or seam on the surface of something. Both terms are used to describe the same geological feature, which is a coal-seam.