often a type of grotesque creature

A monster is any scary creature in fiction. They are usually found in legends or horror stories. They are often ugly and may make people and other creatures scared. They also eat people sometimes. A monster could be anything really, like a vampire or a witch or even a werewolf. Sometimes these creatures aren't bad or monsters as you would say because some protect other people. Anyhow anything can be a monster or a creature including you.

Artist representation of a yeti or Bigfoot.