Haploid refers to the presence of a single set of chromosomes in an organism's cells. Sexually reproducing organisms are diploid (i.e., having two sets of chromosomes, one from each parent). In humans, only the egg and sperm cells are haploid.
The term haploid can also refer to the number of chromosomes in egg or sperm cells, which are also called gametes. The number of chromosomes in a single set is represented as n, which is also called the haploid number. In humans, n = 23.