What is double fertilization in angiosperms?

Double fertilization:

1. Two male gametes are released from the pollen tube.
2. The zygote is formed when one male gamete fertilizes the egg ( syngamy).
3. A triploid main endosperm nucleus is formed when the other male gamete joins with the central cell's two polar nuclei.
4. The merging of three haploid nuclei is known as triple fusion.
5. The occurrence of two types of fusions, triple fusion and syngamy in an embryo sac, is known as double fertilization.