what is hantu?

Just had lunch with my colls. Had a good laugh listening to the stories of my coll's kids. One of them has a pair of twins. Currently, the twins are so obsessed with Ultraman and they fight with each other everyday pretending to be Ultraman & aliens. Another coll asked us does a "boo lang sai" (lion from lion dance) have teeth? Uh-oh, i think so, it's an animal afterall. Another shared with us another story about her girl. Her girl came back one day to ask her, what is "hantu". Not wanting to scare the girl, she told her girl hantu = pretty girl. Hahaha...imagine her girl tells her mum this "mak cantik macam hantu" innocently :D