Here are some other useful and related terms.
Analogy: Similes and metaphors are mostly used in creative writing to deliver strong imagery and to entertain. However, we can also use them when making an argument or trying to get our point across. When we do this, it's called an analogy or an analogous statement.
Books and movies are like apples and oranges. They both are fruit, but taste completely different. (Stephen King)
People are like stained-glass windows. They sparkle and shine when the sun is out, but when the darkness sets in, their true beauty is revealed only if there is a light from within. (Elisabeth Kübler-Ross)
Love and guilt are like ham and eggs. So many people enjoy them together, but there’s no rule saying you must have one with the other. They don’t even come from the same animal. (Rachel Hartman)
Just as music is noise that makes sense, a painting is colour that makes sense, so a story is life that makes sense. (Yann Martel)
Allegory: When an entire book or story is a metaphor for something else, we call it an allegory - it is allegorical.
An example of this is the novel Animal Farm by George Orwell. In the story, the existing power structure on the farm breaks down when the animals rebel against their human owner. In the aftermath, the pigs take over power and maintain order through the guard dogs. The pigs soon become more oppressive leaders than the humans were. The story is allegorical in many ways.
Firstly, through its imagery. An insult in English is to call someone a 'selfish pig,' and dogs are known for their loyalty but not always their intelligence, following orders without question. So, in this way, animals symbolise personality types. You can learn more about the metaphorical and symbolic aspects of Animal Farm in this 11-minute video.
At the same time, the book explores the way in which power corrupts. It was hugely influenced by the events of the Russian Revolution (1917-1923), but by making this an allegorical tale, rather than directly referencing the revolution, the story can be applied to any political system anywhere in the world. It makes it a universal cautionary tale, and this is why allegories are useful. Many traditional stories, legends and fables use allegory to make a moral point. Because they are not tied to specific true-life events, they remain pertinent and get passed down from generation to generation.
Euphemism: A euphemism - when we speak euphemistically - is when we moderate our language to be less blunt or direct.
We do this when we are trying to be polite, but it can also make the meaning of what we are saying less obvious.
Blunt: She's dead
Euphemism: She's passed over -or- she has gone to a better place
Blunt: He was fired from his job
Euphemism: He was let go
Blunt: You're drunk
Euphemism: You look a little unsteady on your feet
Blunt: Did you fart?
Euphemism: Did you pass wind -or- did you make a booty tooty?