Nucleotides are the building blocks of nucleic acids like DNA and RNA. Each nucleotide consists of a sugar, a phosphate group, and a nitrogenous base. When two nucleotides join, the phosphate group of one nucleotide forms a covalent bond with the sugar group of the next. This specific bond is called a phosphodiester linkage because it involves two ester bonds (diester).

The reaction can be represented as: $\mathrm{Sugar}-\mathrm{OH}+\mathrm{HO}-\mathrm{Phosphate}\to \mathrm{Sugar}-O-\mathrm{Phosphate}+{\mathrm{H}}_2\mathrm{O}$

Final Answer: Phosphodiester linkage