The term 'haploid' is descriptive of a nucleus, cell, or organism that has only a single set of unpaired chromosomes, i.e. half the number of chromosomes found in diploid cells. The number of chromosomes present is termed the haploid number.
All human cells except gametes are diploid, having 46 chromosomes. A gamete (ovum and sperm) is haploid, having 23 chromosomes.
Most fungi, protists, and algae are haploid, as are some insects and bryophytes, certain stages in the life cycle of plants, and the gametes (reproductive cells) of all organisms. Haploid cells are produced by meiosis. The fusion of two haploid cells restores the normal (diploid) number. See also alternation of generations.