In language, idiom conflation is the amalgamation of two different expressions. In most cases, the combination results in a new expression that makes little sense literally, but clearly expresses an idea because it references well-known idioms. All conflations fit into one of two major categories: congruent conflations and incongruent conflations.
Congruent conflations are the more ideal (and more sought-after) examples of the concept. These occur when the two root expressions basically reflect the same thought.
Incongruent conflation occurs when the root expressions do not mean the same thing, but share a common word or theme.