Nucleus

The Nucleus (noun) is a organelle of a Eukaryotic Cell. It is covered with a double layered membrane and houses Chromatin (basically DNA and some proteins) and a amorphous body called nucleolus. It is one of the most important parts of the Cell as it is a site for DNA replication, Ribosome formation (small particles which make proteins), and housing the DNA.

The Nucleus of a typical plant cell gets pushed to a side by its large vacuole.