It's- kind of a thing from home. It's this idea that humans can enjoy and appreciate something that is sort of humanoid but obviously not, like a cartoon or a blocky robot. The more human it gets, the more comfortable people get with it because it's like them. Then there's this weird area where something is almost human, but there's something about it that seems so off that people can't stop focusing on it. The gap between that and a true human is the uncanny valley.

[Here, have a little doodle to accompany the tl;dr.]