What is "external fertilization"

n. (context biology English) Fertilization involving the fusion of the male and female gametes outside the bodies of the reproducing individuals.

External fertilization is a strategy of fertilization in which a spermcell unites with an egg cell in the open, rather than inside a specialized organ within the body of a parent. Releasing eggs and sperm into water is called spawning. In contrast, internal fertilization takes place inside the female after insemination through copulation. Among vertebrates, most amphibians and fish utilise external fertilization, with eggs being liberated into the environment by the female and sperm by the male. In many cases, a clutch of eggs is laid and the male immediately liberates his sperm in close proximity.

Many invertebrates reproduce by external fertilization. In aquatic environments the sperm typically have flagella and swim to the egg. Vast numbers of gametes may be involved and some organisms such as corals, synchronise the emission of their gametes to increase the chances of successful fertilization. Plants use internal fertilisation apart from a few aquatic non-vascular plants.