A normal human body cell usually contains 23 pairs of chromosomes.
That total is 46 chromosomes: 22 pairs of autosomes and one pair of sex chromosomes. One chromosome in each pair is inherited from the mother and the other from the father. The sex-chromosome pair is commonly XX or XY, although variations also occur in human biology.
This count applies to most diploid somatic cells, not every human cell. Mature red blood cells have no nucleus, and human egg and sperm cells are haploid, carrying 23 unpaired chromosomes. When an egg and sperm fuse, their chromosome sets combine to restore the diploid number.
Chromosomes are DNA-protein structures that package genetic material. Changes in chromosome number or structure can affect development and health. Down syndrome, for example, is usually associated with an extra copy of chromosome 21, making three copies instead of the usual pair.