The canyon air volume is the air contained within the walls, ground and 'lid' of the canyon, the lid being an imaginary boundary at roof level.

A real or imaginary boundary separates the system from the rest of the universe, which is referred to as the environment or surroundings (sometimes called a reservoir.)

It was just a thing of the mind, a boundary imaginary rather than real, but in looking around this area he saw the same thing.

The imaginary boundary formed by the cordon was not to be crossed by a prisoner.

"I understand everyone's parochialism in wanting to have the airport in their boundary, but imaginary boundaries shouldn't be the guiding factor in a decision of this magnitude," Mr. Baise said.

The imaginary boundary of my world had changed.

The solar envelope regulates development within imaginary boundaries derived from the sun's relative motion.

The imaginary boundary they defended was a surface trillions of square kilometers in area, mostly empty space.

The lake is also an imaginary boundary of the Rendille and Borana and Oromo to the Turkana land.

Human cultures are, according to Benhabib, the constant change of imaginary boundaries.