Here's why:

* DNA is organized into chromosomes: DNA is a very long molecule, and to fit inside a cell's nucleus, it's tightly wound around proteins called histones. This organized structure is called a chromosome.

* Humans have 23 pairs of chromosomes: Each human cell has 23 pairs of chromosomes, with one chromosome from each pair coming from the mother and the other from the father.

While "strand of DNA" is technically correct, "chromosome" is the more specific and widely used term.