One of the more savage set of races you will find in the universe of Warhammer, Greenskins are not actually one species, but several green-skinned species which are grouped together into one group. These roving marauders do not have a home of their home, but do make homes out of the homes of those which they conquer, forming ramshackle arcitecture easy to distinguish from the other, more complex structures created by many of the other races.
The greenskin battle cry is "Waaaaah!", also the name of a large battlegroup. Battlegroups will only form on the odd occassion that one charismatic greenskin takes it in their head to become a warboss. When they form one of these groups, they quickly become destruction incarnate, destroying whatever stands in their path.
 Game Involvement
Orcs are one of many races in the Warhammer universe, and seem to be in some ways similar to their 40k cousins, the Orks. As such, the greenskins of this time have been involved in a few games during the medieval settings.
 Warhammer Online: Age of Reckoning
The greenskins are major players in the Warhammer Online: Age of Reckoning game, the first successful MMO to have been released from this franchise. In Warhammer, the greenskins have formed together under the rulership of the Warboss Grumlock, and his counterpart, Goblin Shaman Gazbag. In this game, the greenskins join the Dark Elves and the forces of Chaos as a member of the realm of destruction, although it is suspected that these who have lead their clan, "Bloody Sun Boyz", to success, are being guided by a hidden hand in this new cause.
Their racial enemy in this game are the Dwarves, a dimunative race which shares some characteristics of the smaller Greenskins, but with the strength to handle some of the larger ones.
 Member Races
There are several different races which make up the larger group known as the Greenskins. These are the Orcs, the goblins, the hobgoblins, and the snotlings.
Out of all the greenskin species, the largest of all the races is the Orcs. The orcs, large, muscular, and fierce fighters, often make up the front of the forces the enemy sees. However, these greenskins are not the smartest of species. One of the most infamous examples of the stupdidity of the Orcs is the tendacy of the species to catapult their own men over walls -- or, more often, into them, and other assorted hard objects which result in the flingee's death.
An orc lives to fight, with a social structure built around strength. Orcs disdain those who are weaker than they, and are only too willing to quash those under their might. Those who are especially skilled at doing so will eventually outdo those who challenge them in the tribe, and will assume the title of warboss. Those with the title of Warboss tend to be the strongest and most charismatic of the tribe, and those who are especially strong can even lead their kind into battle. Even stronger ones, may even be able to lead their race.
Like all greenskin species, the Orcs are androgenous, and are actually born from a form of budding out of plant life. There is no such thing as a female Orc. Those who are especially strong, have a skin colour which slides towards black, marking them as the strongest, most savage, and most skilled at slaughter out of the members of their race.
More dimunative, these species make up the larger component of the greenskin race alongside the Orcs. Although smaller, this species tends to be able to be able to maniulate their larger cousins, the Orcs, into doing their bidding. The members of this species tend to take the rolls of the intellectuals amongst their race.
Through constant bullying of the Orcs, this race has grown an insidious cunning which has made them an incredibly intelligent race. This leads them to have the technological skill of the two races. While perhaps not as skilled as the mechanics within Dwarven society, the technological skill of the Goblins should not be overlooked.
Greenskins are rather unqiue in fantasy universes in that they truly do not have a female side to their species. They are grown from plants, and erupt from them via a process of budding. Therefore, there is no such thing as a female ork, which has lead to jokes about their species' famously violent nature, and also curiosity as to whether or not there is actually a male side either.
The culture of the geenskins is hierarchal, with those who are stronger or more cunning amongst their kind being able to wind their way up the ladder of their own tribe, and those who head the tribes consistently try and expand their power over the others. For Orks, this is based more in brute strength, especially for black orks. For the goblins, this is based more in their ability to be cunning.