Haploid refers to the presence of a single set of chromosomes in an organism's cells. Sexually reproducing organisms are diploid (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. In humans, gametes are haploid cells that contain 23 chromosomes, each of which a one of a chromosome pair that exists in diploid cells.