Ribonucleic acid (RNA) is a polymeric molecule (see below) that is essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and DNA (Deoxyribonucleic acid) are both nucleic acids. Nucleic acids, along with lipids, proteins, and carbohydrates, are the four major macromolecules that are essential for all known forms of life.
Note: a polymer is a large molecule, or macromolecule, that is composed of millions of repeated linked units. Each link being a relatively light and simple molecule.