The body contains two types of cells - haploid cells and diploid cells. The difference between them is the number of chromosomes that the cell contains.
All animal cells have a fixed number of chromosomes in their body cells which exist in homologous pairs (2n). Each pair of chromosomes consists of one chromosome from the mother and the second from the father. During the process of meiosis (cell division for sexual reproduction), the sex cells divide to produce "gametes" which then contain only one set of the chromosomes (n).
When the male and female gametes fuse during fertilization and zygote formation, the chromosome number is restored to 2n again.
Haploid cells are the gametes which contain one set of DNA (n), which is 23 chromosomes in humans, whereas diploid cells are the body cells that contain two sets (2n), or 46 chromosomes.