Android
An android is described by most scientific outlets and professionals as any kind of robot designed to phisically resemble a human being, both in their appearance and its behaviour. The concept of machines acting and looking like humans has been a very common idea for discussion in science fiction and scientific speculation, and the concept has been explored in many ways throughout history. This, of course, has meant that the idea has been developed and used by many authors of science fiction and fantasy writing, and it's frequently represented in many tabletop games and settings.
It is important to take into consideration that the original concept doesn't necessarily need the android to be an electronic-based creation, that idea appeared alongside the developement of computer science and AIs. Because of this, the idea of android is not limited to sci-fi settings, but it can also be included in fantasy settings.
Do not confuse with Cyborgs. A Cyborg is an amalgamation of a living being with artificial parts, whereas the android is fully artificial. Take that, whoever translated Dragon Ball!
Origins of the concept
The idea of machines looking and acting like us is not a recent topic of discussion. The first people to develop this idea were the ancient greeks with the automatons, complex artificial constructs designed to follow a series of instructions, usually resembling the human form. One of the most famous of them was Talos, a bronze automaton designed and created by the god Hephaestus (although in some versions the author is a mortal inventor) as a request by Zeus, and with the task of protecting Zeus's lover Europa. Talos's job consisted in guarding the island of Crete to avoid any potential threat to reach Europa.
Also one of the most famous takes of the android is the jewish tale of the Golem. A being magically animated created out of clay, it appears frequently in ancient jewish folklore, although the most famous version of the myth is the Golem of Prague, where a rabbi created a golem to protect the jewish community of the city, and had to dispose of the thing after that, usually after a series of violent events.
The first takes of the modern android, a machine based on science and technology instead of magic or divine powers, appeared during the XIXth century in some speculative histories about "mechanical dolls". The term would not become popular until George Lucas brought the word "droid" into Star Wars. If a droid was just a robot, an android is a droid that looks like a human. Anthrop- is the greek root for human being, droid is robot, you mix the two together and you get android. Of course, the idea on modern media was older than that (see the movie Metropolis for a very early interpretation in cinema), but they usually just used the world robot, which is not as precise as it should be.
Actual developement of androids
Nowadays, the developement of human-like robots has risen in popularity, although the results usually fall right into the uncanny valley. Seriously, just look at some of those japanese androids they show on those technology showcases, and tell me you don't get the creeps. The investigation also focus on the AIs, in particular those that allow self-learning. But as of now, they look and act very dumb. So your dream of getting your own robot girl is still too far. Don't lie, you want one.
Examples of androids in D&D
I don't play D&D, you fill this part.
Examples of androids in Warhammer Fantasy and AOS
I don't play them either, you fill this part too.
Examples of androids in Warhammer 40k
In the 40k lore, mankind once had to wage war against its mechanical creations, Terminator Judgement style but on steroids. After that, humanity is so paranoid of this happening again that they totally forbade the creation of AIs. They create humna-like robots though, at least in the sense that their shape resembles a humanoid being. The best exampe of this are the titans, massive war machines that praise the holy human form by resembling the shape of a human (two arms, to legs, a head. That's it. So much for holy human form). In general, though, the Imperium relies much more in cyborgs, both in the way of servitors and the Adeptus Mechanicus. Chaos could in theory create some form of automata, but they rather make chaos s-THINGS! Yes!
Anyway... Outside of Mankind, the other factions that use their own shape to make artificial beings. In general, any faction that's vaguely humanoid builds constructs that resemble human forms. The best example of an android in the traditional sense are the Tau, who use massive amounts of robots and can create AIs good enough to pass as living, thinking beings.
Famous examples of androids in popular culture
- Do Androids dream of electric ships? (or Blade Runner, if you like films more). Humans create artificial humans as slaves, and after a revolt they hunt them all down. This is an interesting case because they are organic beings, but still artificially made, so the definition is just barely apt in this case.
- I, Robot. In the classic Isaac Asimov's short story, there are some robots that could be described as android.
- Metropolis. Mad science creates a robot that resembles a humble woman to bring chaos and ruin to the city.
- The day the Earth stood still. An alien brings a doomsday machine in the form of a human to "peacefully" stop all wars on Earth.
- Terminator. Machines rise against humanity, using human-like assassins to kill the remaining human beings.
- Marvel Comics. Characters like Vision or Ultron are thinking robots in human-like form.