Chromatin is the 3-dimensional structure of DNA, which is tightly packed inside each cell.
Amazingly, in every human cell, DNA is compressed thousands of times so it can fit into the nucleus. How is this possible? It’s because the DNA is wound up, like a spool of thread, around a scaffold of proteins called histones, creating a structure called chromatin.
When the information stored in DNA is not in use, chromatin is wound up and tightly packed. But sometimes the cell needs to access the information, which means it has to unpack chromatin.