The term "nucleobase" refers to the fundamental building blocks of DNA and RNA molecules. These nitrogen-containing compounds are responsible for providing the genetic information that dictates the characteristics and functions of living organisms. Synonyms for nucleobases include nitrogenous bases, purines, pyrimidines, and nucleosides. Purines and pyrimidines are subcategories of nucleobases that differ in their chemical structure and are characterized by the presence of either two carbon-nitrogen rings (purines) or one carbon-nitrogen ring (pyrimidines). Nucleosides are compounds consisting of a nucleobase attached to a sugar molecule and are important intermediates in the synthesis of nucleic acids. While the term nucleobase may be unfamiliar to some, these synonyms are commonly used in biochemistry and molecular biology research.