The male germ cell in animals and plants, the
   essential element in fertilization; a microscopic animalcule-like
   particle, usually provided with one or more cilia by which it is
   capable of active motion. In animals, the familiar type is that of a
   small, more or less ovoid head, with a delicate threadlike cilium, or
   tail. Called also spermatozoon. In plants the more usual term is
   antherozoid.