This is an example of an idiom. When we say it's raining cats and dogs what we really mean is that it is raining very hard.
An idiom is a phrase that is not taken literally. Another example would be "to kill time".

Personification is when we given human characteristics to inanimate objects. The sun doesn't really smile on us. Another example would be "the tree moaned in the wind".

A metaphor is a figure of speech in which a term is applied to something to which it is not literally applicable in order to suggest a resemblance.

A simile is a figure of speech in which two unlike things are explicitly compared, often using like or as.

Hyperbole is an intentional and obvious exaggeration. It is often used for dramatic effect.

One of my personal favorites, an oxymoron uses contradiction in a compressed manor. More examples include "kill them with kindness", "pretty ugly" and "clearly confused".

Onomatopoeia is defined as the formation of a word by imitation of a sound. Can you think of other examples?