Haploid and Monoploid
The haploid number (n) is the number of chromosomes in a gamete of an individual. This is distinct from the monoploid number (x), which is the number of unique chromosomes in a single complete set. Gametes (sperm, and ova) are haploid cells. The haploid gametes produced by (most) diploid organisms combine to form a diploid zygote. For example, most animals are diploid and produce monoploid haploid gametes.
During meiosis, sex cell precursors have their number of chromosomes halved by randomly "choosing" one homologue, resulting in haploid gametes. Because homologous chromosomes usually differ genetically, gametes usually differ genetically from one another.
All plants and many fungi and algae switch between a haploid and a diploid state (which may be polyploid), with one of the stages emphasized over the other. This is called alternation of generations. Most fungi and algae are haploid during the principal stage of their lifecycle.
Male bees, wasps, and ants are haploid organisms because of the way they develop from unfertilized, haploid egg cells.
In humans, the monoploid number (x) equals the haploid number (n), x = n = 23, but, in some species (especially plants), these numbers differ. Common wheat has six sets of chromosomes in the somatic cells, derived from its three different ancestral species. The gametes of common wheat are considered to be haploid, since they contain half the genetic information of somatic cells, but are not monoploid, as they still contain three complete sets of chromosomes (n = 3x).
Read more about this topic: Ploidy