The Pure Land imagined by most Pure Land Buddhist schools is the Western Pure Land of Amida Buddha (also known as Amitabha). As a bodhisattva, Amida undertook a vow (called the Primal Vow) that he would save all sentient beings (the Bodhisattva Vow), and that he would create his Buddha land as a great paradise, where all beings could enjoy good lives and the teachings of the Buddhas. The Western Pure Land is conceived of as a land of physical, intellectual, and spiritual pleasure, where all beings are born in bodies without flaw. Having been born in the Pure Land, karmic 'backsliding' is impossible; one will never again be born in the lower realms of existence. All beings born in the Pure Land will learn the teachings of the Buddha, and become enlightened
The Pure Land is described in the Sukkhavativyuha Sutra. It is said to be a beautiful world, filled with gardens and jewels. The voice of the Buddha is heard everywhere, like divine elevator music. It is a realm of heaven, where suffering and strife do not come.
Pure Land Buddhism is often seen as a break from most schools of Buddhist thought. It places the power of salvation not in jiriki, self power, but in tariki, other power. The creation of the Pure Land schools and the existence of the Pure Land itself is taken as evidence that Buddhism has entered the age of decline (called mappo in Japanese); salvation is no enlightenment is no longer possible in the corrupt world, so salvation must be sought through the intervention of the Buddha Amida.
One comment on sensei's wu above- not all schools believe that it is the chanting of the nembutsu that causes one to enter the Pure Land. Shinran, founder of the Jodo Shin Shu school, believed that all beings were ultimately saved purely by the compassion of Buddha Amida, and that any action taken by mortals was purely a result of karma. So while the chanting of the name of Amida was a way to show appreciation for the acts of compassion that had made salvation available, the chanting itself was incapable of causing a change in the fate of the practitioner. One could only wait out their karma, sure in the hope that Amida would save them in the fullness of time.
The Pure Land sounds a great deal like heaven, and the vow of Amida much like Christian conceptions of salvation. It would be interesting to hear what, if anything, was the connection between the rise of the Pure Land belief and the spread of Christian teachings. Certainly, modern Pure Land churches and temples in the United State look more like Protestant churches than anything else, but this is the result of decades of assimilation.