General: uncanny valley
This term refers to characters that are lifelike yet not lifelike enough to really seem alive to the average viewer. Causes of this are often because of dead-looking eyes, stiff facial expressions, and a plastic-like appearance in general. The effect can lead to outright revulsion or just a disconcerting effect upon viewers.
The term is named after a graph done by Japanese roboticist Masahio Mori in 1970, describing the faces of robots as graduated upon a line graph. Halfway up the first slope is labelled 'toy robot': devices that are non-human while also non-threatening. The lowest peak is labelled 'Bunraku puppet'. The highest peak is labelled 'human'. Between them is a deep valley, the lowest point of which is labelled 'moving corpse'.
Please note that the term is subjective. What does or doesn't give you the willies may not do the same for someone else. As well, this term isn't exactly the same as 'creepy' and 'nightmare fuel'; something can be just disconcerting without being horrifying.