haploidy

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 are monoploid, and these can combine to form a diploid zygote. For example, most animals are diploid and produce monoploid gametes.