Thymine is one of the four bases which make up DNA molecules. It uses two hydrogen bonds to form a complementary base pair with Adenine (A). Thyamine is not present in RNA, instead it is replaced by the base Uracil. Thymine is a pyrimidine; a pyrimidine is a heterocyclic aromatic compound.
Thymine combined with deoxyribose creates the nucleoside deoxythymidine, which is synonymous with the term thymidine. Thymidine can be phosphorylated with one, two, or three phosphoric acid groups, creating, respectively, TMP, TDP, or TTP (thymidine mono-, di-, or triphosphate).