Which base is NOT found in RNA?

In RNA, the bases that are present include adenine, guanine, and cytosine, along with uracil. Thymine, however, is the base that is found in DNA and not in RNA. This distinction is important because it highlights the different roles and structures of DNA and RNA. While DNA contains thymine, RNA replaces thymine with uracil. Understanding this difference is fundamental in genetics, as it reflects the biochemical variations between nucleic acids and how they function within the cell.