1.
a. The use of words to express something different from and often opposite to their literal meaning.
b. An expression or utterance marked by a deliberate contrast between apparent and intended meaning.
c. A literary style employing such contrasts for humorous or rhetorical effect.
2.
a. Incongruity between what might be expected and what actually occurs
b. An occurrence, result, or circumstance notable for such incongruity.
Example (meaning 2): you post an entry warning people against scammers targeting interpreters, and a Mrs. Rose adds a comment to it offering you $10,000,000.00 (originally intended to buy a cocoa processing machine) in exchange for a bit of help.