The fusion of the male gamete with two polar nuclei inside the embryo sac of the angiosperm is known as triple fusion. Since there are three haploid nuclei, the process is known as triple fusion.
The product of the triple fusion process is the formation of the endosperm.
Endosperm tissue is present inside the seeds of the flowering plants which is then used in the fertilization. It provides essential nutrients to the in form of starch.