1) The material of chromosomes. It is a complex of DNA; histones; and nonhistone proteins (chromosomal proteins, non-histone) found within the nucleus of a cell.

2) The genetic material of the nucleus, consisting of deoxyribonucleoprotein, which occurs in two forms during the phase between mitotic divisions: a) as heterochromatin, seen as condensed, readily stainable clumps; b) as euchromatin, dispersed lightly staining or nonstaining material. During mitotic division the chromatin condenses into chromosomes.

3) Chromatin is a substance within a chromosome consisting of DNA and protein. The DNA carries the cell's genetic instructions. The major proteins in chromatin are histones, which help package the DNA in a compact form that fits in the cell nucleus. Changes in chromatin structure are associated with DNA replication and gene expression.