Orks are a brutal race of savages who exist only to fight, kill and die. In Warhammer Fantasy, they are the typical horde based creatures who wage war for the sheer pleasure of bloodshed. In Warhammer 40,000, they are just as the same, except they are space-faring aliens who have access to crude and barely functioning equipment that is powered by their gestalt psychic powers (which they are unaware of).
Whats interesting is that they are a single gender race. They neither have females or genitalia. Their way of reproduction is that when they die, they release spores on the ground which would then grow into a variety of Orkoid specimens, whether they be ordinary Orks (or those with unlocked Physic powers), the smaller yet more intelligent gretchin, or the vicious and hound like squigs. However, this still hasn't stopped artists from depicting them with genitalia