Did Lord Buddha teach, or do Buddhist sects teach, about Ghosts?

The existence of Ghosts is taught in many religions. And Buddhist sites (mainly Tibetan Buddhists) claim the existence of "Hungry Ghosts". However I didn't see sites saying that the Buddha claimed that ghosts exist. Did Lord Buddha teach about Ghosts, or is it only Buddhist sects which teach that? Also do ghosts exist here on this earth, do they affect or possess people, are they visible? Or are they only in some other real of existence?