HCN, or hydrogen cyanide, is a polar molecule. It consists of two polar bonds whose polarities line up in the same direction, thus conferring an overall partial positive charge on one end of the molecule and a partial negative on the other end.
Hydrogen cyanide is a linear molecule with carbon between hydrogen and nitrogen. The covalent bond formed between carbon and hydrogen is polar because carbon is more electronegative than hydrogen and it attracts the bonded electron pair closer to itself, thus giving hydrogen a partial positive charge. Nitrogen, which forms a triple bond with carbon, is more electronegative than carbon and pulls the bonded electron pairs towards itself, thus obtaining a partial negative charge. Since the molecule has a different partial charge on each end, it is a polar molecule.