Conscience was a personality trait that helped an individual determine right from wrong.
"Live without conscience" was one of the commandments which Daleks were bound to follow, and, as such, was engraved on the plaque of the "Dalek creed" which was found by humans near a crashed Dalek spaceship. (PROSE: The Dalekreed)
Among other things, Miss Kizlet was able to control the conscience in the people whom she had uploaded into the data cloud. By manipulating a numerical values for conscience on her tablet, she was able to, as one of her underlings once said, "hack into" people's personalities and instantly change their conscience metric. (TV: The Bells of Saint John)