Chromatin is a complex of DNA and proteins found in eukaryotic cells, with the function to pack DNA in more compact shape and to prevent DNA damage. One of the main components of chromatin are proteins called histones. Histones are directly responsible for DNA package to form structures called nucleosomes. Chromatin can be found in its active form-euchromatin (tuned on genes) and inactive-heterochromatin (turned off genes).
Chromosomes are organized structures of DNA which are visible in certain stages of cell cycle (such as metaphase when they are aligned). Every chromosome is copied once during the S phase of the cell cycle. It is then found in an X-shaped structure (centromere is located in the middle of the chromosome and two-arm structures are the original chromosome and the copy -sister chromatids).