Orcs are a fictional race seen in many modern fantasy mediums (such as books and games), made of large, savage, and sometimes irredeemably evil humanoids. Created by J.R.R Tolkien, and their name was intended to be based on Old English words for "demon" or "ogre."
In Tolkien's works, smaller Orcs are sometimes referred to specifically as "Goblins," so in this sense one may consider an Orc to be a larger and more brutish type of Goblin, however outside of Tolkien's works this is rarely true, and Orcs are often made out to be a distinct race from Goblins, although in the Warhammer setting Orcs and Goblins are related races, part of a larger family of races known as "Greenskins."
Orcs are almost always savage and/or warlike, and are usually made out to be evil, unintelligent and pitiful monsters, and are often a creature simply used for "slaying fodder" for quests. However in the Warhammer settings Orcs or "Orks" are playable armies, and there is a sense of whimsy and glorified stupidity about them.
The Warcraft setting they are also playable; and their bloodlust and depravity came from being controlled by a demon curse which they have freed themselves from, and now have a sense of honour. In some other settings they are also from time-to-time given this "noble savage" image.
"The orcs are coming!"
"Well don't just stand there, slay them all!"