1) Uracil (U) is one of four chemical bases that are part of RNA. The other three bases are adenine (A), cytosine (C), and guanine (G). In DNA, the base thymine (T) is used in place of uracil.

2) A pyrimidine base (C4H4N2O2) that is one of the four bases coding genetic information in the polynucleotide chain of RNA.