Talk about syngamy.

Syngamy is the process of fusion of two gametes (of different sexes, male and female) to produce a diploid zygote which later becomes the new individual. Syngamy can be divided into two sequential stages: plasmogamy (fusion of the cytoplasm of two parent cells) and karyogamy (fusion of two haploid nuclei to produce a diploid cell). Usually, plasmogamy is immediately followed by karyogamy. In some systems of reproduction, karyogamy is delayed; the two haploid parental nuclei cohabit without fusing the cell (dikaryotic cell (n+n) or a dikaryon) that results from plasmogamy.