Hair is something that grows on people's heads. It is also found on the rest of your body, but it is very very fine and can be hard to see (depending on the person!). The hair that grows on animals like cats and dogs is actually called fur, and the hair on sheep is called wool. The hairy stuff on even stranger things like spiders and some plants isn't hair either, just something that can look like hair and helps to protect whatever it is growing on. Hair on your face is called a beard or moustache.