A haploid is a cell or organism that contains a single set of chromosomes, represented as n. In humans, for example, haploid cells are the gametes (sperm and eggs), which each contain 23 chromosomes. This contrasts with diploid cells, which have two sets of chromosomes (2n), one inherited from each parent. Haploidy is crucial for sexual reproduction, as it ensures that when gametes fuse during fertilization, the resulting zygote has the correct diploid chromosome number.