Here's why:

* DNA itself is a long, thin molecule.

* Chromatin is the complex of DNA and proteins that makes up chromosomes.

* The proteins in chromatin, particularly histones, help to package and organize the DNA into a more compact form. This winding and packaging process is essential for fitting all of the DNA inside the nucleus of a cell.

So, when you see the term "wound up DNA," you're essentially talking about chromatin.