In the Terminator universe, a terminator is a formidable "cybernetic organism", robotic assassin and soldier, designed by the military supercomputer Skynet for infiltration and combat duty, towards the ultimate goal of exterminating the human resistance. Terminators are indistinguishable from humans, can speak naturally, copy the voices of others, read human handwriting, and even sweat, smell, and bleed.
One of the few giveaway signs is that a dog will bark continually at a terminator. The human resistance uses dogs to help spot them. A trait persistent throughout the series is the faint red glow of the "robotic eyes" when online, which dim to nothing when a terminator shuts down. In all four movies, the lack of the glow has been used to show when one is out of action. The trait is so characteristic that light-up eyes are often found on Terminator merchandise, with some even replicating the dimming/reillumination effect that occurs during shut down or start up. Guardian terminator Cameron states to John Connor in Terminator: The Sarah Connor Chronicles episode "The Mousetrap", that terminators' densities deny them the ability to swim. T-888 Cromartie demonstrated in the same episode, however, that they can survive submerged and walk along the bed to the shore. The prototype terminator Marcus Wright in Terminator Salvation did demonstrate the ability to swim, though he is the only one of his type.