When people think about what Freddy is, the word ghost doesn’t immediately jump to mind. And over the course of the Nightmare on Elm Street series, he became something much more than a ghost (we can chat about the Dream Demons another time). But at the start of the Elm Street saga, Freddy Krueger was definitely a ghost.
Specifically, a vengeful spirit. Like the spirits in The Ring, Poltergeist or the Fog, the spirit of the Springwood Slasher came back to seek revenge for the wrongs that were done to him in life. In this case, it was the fact that the parents of Springwood burned Freddy alive when he got off on a technicality after abusing and killing almost two dozen children. So, he came back to seek his revenge on Springwood, haunting and killing the teenagers around his old stomping grounds–the Elm Street neighborhood.
What made Freddy stand out from your run of the mill ghost was his modus operandi–he haunted his victims as they slept, subjecting them to terrifying nightmares and bringing truth to the belief that if you die in your sleep, you die in real life, as well. Those who were haunted by him had to avoid falling asleep at all costs, an impossible task, as most of them found out the hard way.