A gamete is a sexual cell, in the case of men it is the sperm and in the case of women it is the egg. Both male and female gametes have to fuse in the process known as fertilization to give rise to an embryo and for pregnancy to take place.
Gametes are haploid cells, i.e. they have 23 chromosomes, half the number of any other cell. This means that when the egg fuses with the sperm, the chromosome endowment of the human spice can be re-established: 46 chromosomes.