The fertilization of an ovum by more than one sperm.
The ovum fertilized by more than one sperm results in having more than two copies of each chromosome -- one from the ovum and one each from the sperms. The resulting zygote is often inviable.
Word origin: from polyspermia » Gk polyspermía abundance of seed + -y.
Related forms: polyspermic (adjective)
See also: fertilization.