The non-staining or slightly chromophilic, liquid or semi-liquid, ground substance of the interphase nucleus and which fills the nuclear space around the chromosomes and the nucleoli. Little is known of the chemical composition of this ground substance, which is not easily defined. It may be called "karyoplasm" when it is gel-like, and "karyolymph" when it is a colloidal fluid, but generally the terms are synonymous.
Similar to the cytoplasm of a cell, the nucleus contains nucleoplasm or nuclear sap. It is enveloped by the nuclear membrane or nuclear envelope. The nucleoplasm is a highly viscous liquid that surrounds the chromosomes and nucleoli.