An organic molecule consisting of the nitrogenous heterocyclic base (either a purine or a pyrimidine) a pentose sugar (deoxyribose? in the case of DNA, ribose? in the case of RNA), and a phosphate or polyphosphate group.
If just the sugar and base are present, but no phosphate, that is called a nucleoside?. Nucleotides are the monomers of nucleic acids and also play an important role in cellular energy transport and transformations (notably ATP).