Whenever you describe something by comparing it with something else, you are using figurative language. Any language that goes beyond the literal meaning of words in order to furnish new effects or fresh insights into an idea or a subject. The most common figures of speech are simile, metaphor, and alliteration.

Imagery

Language that appeals to the senses. Descriptions of people or objects stated in terms of our senses.

Simile
A figure of speech which involves a direct comparison between two unlike things, usually with the words like or as. Example: The muscles on his brawny arms are strong as iron bands.

Metaphor
A figure of speech which involves an implied comparison between two relatively unlike things using a form of be. The comparison is not announced by like or as. Example: The road was a ribbon of moonlight.

Alliteration
Repeated consonant sounds occurring at the beginning of words or within words. Alliteration is used to create melody, establish mood, call attention to important words, and point out similarities and contrasts. Example: wide-eyed and wondering while we wait for others to waken.

Personification
A figure of speech which gives the qualities of a person to an animal, an object, or an idea. It is a comparison which the author uses to show something in an entirely new light, to communicate a certain feeling or attitude towards it and to control the way a reader perceives it. Example: a brave handsome brute fell with a creaking rending cry--the author is giving a tree human qualities.

Onomatopoeia
The use of words that mimic sounds. They appeal to our sense of hearing and they help bring a description to life. A string of syllables the author has made up to represent the way a sound really sounds. Example: Caarackle!

Hyperbole
An exaggerated statement used to heighten effect. It is not used to mislead the reader, but to emphasize a point. Example: She’s said so on several million occasions

Idioms

Language specific expressions: http://idioms.thefreedictionary.com/