What are haploid cells?

Hint: A cell is called haploid when it carries a single set of chromosomes and is denoted by ‘n’. All the cells of an asexually reproducing organism are haploid, while sexually reproducing organisms have diploid somatic cells, their gametes are haploid in nature.

Complete answer:
Chromosome is the condensed form of DNA which carries all of the genetic material of an organism. The total number of complete sets of chromosomes in a cell’s nucleus is known as its ploidy.
Ploidy can be of 4 types:
-Haploid (n): single set of chromosomes
-Diploid (2n): paired chromosome set
-Polyploid: 3 or more times the number of chromosomes in haploid cell
-Aneuploid: abnormal or not a whole multiple of haploid number of chromosomes
 Chromosomes exist in pairs in diploid organisms, and each chromosome contains an allele of the gene. Since sexual reproduction involves the fusion of two cells, one from both male and female, organisms using this mode of reproduction produce specialised cells called germ cells or gametes; egg and sperm which are haploid, i.e. they contain only half the chromosomes of a normal cell of the same organism. This is done to restore the chromosome count upon fertilization. These haploid cells are produced by meiosis, also known as reductional division. Diploid cells that enter meiosis produce four haploid progenies called meiocytes. Meiocytes differentiate in males and females to produce spermatozoa and ovum respectively.

Note:
Some plants are completely made of haploid cells and are called haploid plants. This happens when gametes of a diploid plant fail to fertilize but somehow grow into a viable individual. Some examples are bryophytes like mosses and liverworts.