An android was a humanoid robot.
In April 1986, several androids based on the appearance of Marty McFly were used by Marcus Irving as a distraction while he stole parts from the DeLorean time machine. By 1997, Irving kept many more android replicas of Doc and Marty at his laboratory.
The androids Marcus created were bipedal, and consisted of a metal endoskeleton covered with fake skin and clothing to give it the appearance of a human. Marcus' androids possessed superhuman strength and were able to inject a knock-out serum into others. A flaw in the androids was the fact that they could not speak, which made prolonged interaction with them suspicious. The face could also be removed if pulled on, which was an instant giveaway as to the android's true nature.