Conceptual blending is where two or more existing concepts are blended together to form a new concept. The blending of the concepts is done in a way that is non-arbitrary. A new concept is formed by taking the meaning of one concept and the form of another. For example, the concept of a car and the concept of a plane are blended to form the concept of a carplane. The concept of a carplane is a non-arbitrary combination of the two concepts. The concept of a carplane is a new concept, with a new meaning, and a new form.
Conceptual blending theory is a theory of how concepts are formed. The theory was developed by Fauconnier and Turner (2002) and was inspired by the theory of conceptual metaphor developed by Lakoff and Johnson (1980). Conceptual blending theory is an extension of conceptual metaphor theory, and conceptual metaphor theory is an extension of the theory of categorization developed by Rosch (1975).

Here are some examples of conceptual blending (where sometimes 2 seemingly disparate ideas are blended): 

Idea 1: Airplane
Idea 2: Car
Blended Idea: Flying Car: A car that can fly.

Idea 1: Hierarchy 
Idea 2: Attire
Blended Idea: Hierarchical attire: In a workplace, a CEO may be wearing a different kind of attire (more expensive) than a director in the company. And a director would probably be wearing more expensive attire than a janitor in the company. So you have a kind of hierarchical attire.

Idea 1: Two-Dimensional Space
Idea 2: Three-Dimensional Space
Blended Idea: 2.5-Dimensional Space

Idea 1: Old
Idea 2: New
Blended Idea: Recycled

Idea 1: Geology
Idea 2: Neurology
Blended Idea: Sediment neurology: When sediments are buried deep under the ground, they can act like a soft layer of neurological tissue in that they will be compressed over time and can get folded and distorted. In neurology, this is called cortical folding. In geology, this is called tectonic folding.

Idea 1: Mathematics
Idea 2: Fecal matter
Blended Idea: Brownian motion: Brownian motion is a type of random motion that happens when you observe the movements of fecal matter (such as protozoans) under a microscope.

Idea 1: More
Idea 2: Less
Blended Idea: Just-Right

Idea 1: Triangle
Idea 2: Square
Blended Idea: Trapezoid

Idea 1: War
Idea 2: Peace
Blended Idea: Armistice

Idea 1:
