Litotes, derived from a Greek word meaning "simple," is a figure of speech

“He was not unfamiliar with the works of Mark Twain.”

• “He was not unfamiliar with the works of Mark Twain.”
• Shows that he is in fact familiar with the works of Mark Twain.
• “I was not a little upset”
• When in fact you mean you were very upset.

“It isn’t very serious. I have the tiny little tumor on the brain”-J.D. Salinger, The Catcher in the Rye

• “It isn’t very serious. I have the tiny little tumor on the brain”-J.D. Salinger, The Catcher in the Rye
• Understating the seriousness of a tumor and its size on the brain.
• "Freedom now appeared, to disappear no more forever”- Frederick Douglass
• Shows that freedom is being materialized