Other forms: nucleoli
A nucleolus is the largest structure within the nucleus of a eukaryotic cell. It's the job of a nucleolus to make RNA and ribosomes.
In a eukaryote, a cell whose nucleus is contained within a membrane, the nucleolus plays a vital role. It's here that ribosomes, tiny cell machines that produce important proteins, are made. RNA — which works by taking the information in DNA and translating it into proteins — also comes from the nucleolus. Nucleolus basically means "smaller nucleus," from a Latin word meaning "little nut."