In the book Ada by Vladimir Nabokov, the term 'Terra' plays a significant role throughout the book signifying an alternate Earth, somewhat occupying the common religious concept of Heaven.

In the book, Terra is a seperate but similar planet which occupies an odd, non-linear groove in space and time. Of course, the whole nature of time comes into question in the book and Nabokov's beliefs.

Essentially, those who live on Earth ("Anti-Terra" or "Demonia" often in the book) go to Terra when they die. Or so is the deduction of Van, a parapsychological researcher who has become familiar with Terra through studying the insane. This belief is shared by Ada, Van's sister and lover, as well as others.

Though details are scarce, Van's beliefs as conveyed in his writing are that Terra is an Earth-like world with a geographical and political setting similar to that of Earth, but approximately fifty years behind. Terra is conveyed by Van as being less like a paradise than his scientific and religious peers would believe.