Webster’s Collegiate Dictionary says ‘horror’ = “A painful and intense fear, dread, or dismay.”
Horror is “intended to scare, unsettle or horrify the reader.” (Steve Bennett, 2009)
It is normally concerned with the supernatural, although not all supernatural stories are horror.
Horror often overlaps with the science fiction and fantasy genres.
(the above is all taken from www.findmeanauthor.com)
An example of horror fiction -
And like a hare from a predator the woman flees into the trees, the voices seeking her out of the darkness. She leaps over fallen trunks, dodges the tangled bushes. The forest is blue with the leaking moonlight, all natural sounds silenced by the night. The woman glances over her shoulder. Nothing. But her heart is loud in her ears now, the trees a colourless blur. She sees handprints come into focus on the trunk of the closest tree. They are human. Small. Deep red in colour. She runs; a ringing of childish laughter coming through the trees, she runs, she grows clumsy, stumbles, forces her way forwards, blind in the web of branches. The crescendo of high-pitched giggling echoes in the night, still surrounding her. The woman’s pearly arms and legs disturb the thorn bushes; she leaves debris from her dress in her wake.