HSN Code 2621 refers to "Slag and ash, incl. seaweed ash 'kelp'; ash and residues from the incineration of municipal waste (excluding slag, incl. granulated, from the manufacture of iron or steel and ashes and residues containing arsenic, metals or metal compounds)." This classification code is essential for identifying materials related to waste management and recycling for import/export purposes based on their nature and intended use. Common products under HSN Code 2621 include seaweed ash, incineration ash, and various residues from municipal waste processing. Additionally, the GST rate for slag and ash under this code supports accurate trade compliance.