Creatures, beasts, inhuman monstrosities, things, whatever else people call them. For all intents and purposes, "monsters" is generally the blanket term used.
However, I find it a little sad that "monster" is the word generally used. That generally evokes such terrible imagery, bringing up pictures of malevolent creatures out there for blood. Even in the world of fantasy and RPG's, "monsters" are generally what are considered the antagonists, and throughout the course of the journey, a giant bloody swath is cut through legions and legions of them. It's only in Sesame Street where the term "monster" is used in a favorable term, and I highly doubt that people will equate Elmo with the Wolf Man. But for the sake of clarity in this post, I'll use the word.
In the heyday of black-and-white horror flicks, sinister music is played while typography in a scary font flashes across the screen, using words like "terrible," "vicious," and "Terrifying!" (exclamation point included). However, the movies usually showed a creature that ended up being misunderstood and was only doing what came natural -- surviving. Was that tentacled, one-eyed beast really that bad or was it just trying to eat? It couldn't help it if it found humans to be a source of food. In the end, it's villainized and killed and the humans are found victorious. This isn't the first time people have viewed and reacted likewise in this situation. Just look at something like the man-eating Great White Shark. It doesn't specifically go looking for humans, but if it's hungry and they're conveniently in the area....
Monsters aren't generally sinister either, and are more a victim of circumstance. Werewolves are a breed that normally can't exactly help what they are. Whether the mythos says the werewolf is born that way or is bitten by another werewolf and turns that way, the person never asked to be that way. Their violence and killing is merely their instinct to hunt and eat.
Godzilla didn't ask to be a giant monster. According to the original film, it was an ancient dinosaur that was awakaned and mutated due to atomic tests. It then wanders about, not understanding the world it's in and leaves widespread death and destruction in its wake.
Zombies (hi, Jade!) can't help it either. Whatever mythos one references, generally one thing is clear -- they couldn't help it. As "Resident Evil" and other zombie films have stated, their brain functions have deteriorated to their most basic of functions and instincts, which is generally the need to eat.
Ghosts can also be misunderstood. They have been portrayed in a variety of ways, and there are just as many reasons out there why they've acted the way they have. Sometimes, they can be friendly ('sup, Casper) or they can be ill-natured. In "Poltergeist," the family moves into a house that was built on top of a graveyard without ever moving the bodies. Sometimes, the ghosts can be more malevolent, as shown in "The Grudge" or "The Ring," but there's at least a reason for the ghosts' hatred.
Granted, there are some evil things and villainy out there associated with monsters. Whatever the mythos might be -- generally when the supernatural is involved -- an evil cause might be the genesis of the creatures' creation. Zombies might be the legions of the undead brought back to life by some evil necromancer. According to some mythos out there, the curse of werewolves ("lycanthropy") was started by the devil.
Also, other monsters are genuinely evil. Dracula, for instance, first started when he turned his back on God. Also, demons and the devil did the same as well, beginning as angels and then leading a war against Heaven. Freddy Krueger was a child murderer who accepted a deal proposed by "dream demons" right before his death. Jason Voorhees...well, from what I understand, his backstory is convoluted, but nevertheless, he turns out to be a bad guy. However, please see that all these instances of evil monsters have proper names attached to them.
It's sadly human nature to fear and attack that which is different and not understood. Granted, in some instances of film, the monsters have ended up being sympathized with or even become the good guys, but for the most part, the history of film has showed another story. However, I find the tale of Frankenstein's Monster a tale more about human nature than about some "monster" -- a man wants to end death, science creates something misunderstood, the creation that never asked to be made is shunned by its creator, and eventually is chased by an angry mob with torches and pitchforks. Sometimes, humans are the biggest monsters of them all...and we're real.