Buddha-kṣetra (Sanskrit, Buddha-field). The sphere of influence and activity of a Buddha. In Buddhist cosmology, each world-system (cakravāla) is the domain of a particular Buddha within which he arises and leads beings to liberation through his teachings. The concept came to prominence in the Mahāyāna on the basis of early speculations about the range of a Buddha's knowledge and the extent of his sensory powers. With the concept of a plurality of Buddhas came the notion of an infinite number of ‘Buddha-fields’ extending throughout the reaches of space in many directions or dimensions. These fields vary in their degree of perfection and are divided into two basic categories, pure and impure. The world we inhabit now is an instance of an impure Buddha-field since beings here are still subject to the basic vices of greed, hatred, and delusion. The most famous of the pure Buddha-fields or ‘Pure Lands’ is the paradise of the Buddha Amitābha in the west described in the Sukhāvatī-vyūha Sūtras, into which all may be reborn by calling upon the name of Amitābha. The existence of these pure Buddha-fields became immensely important in the development of popular devotional Buddhism, especially in China and Japan.

A Dictionary of Buddhism, Oxford University Press, 2003, 2004 (which is available in electronic version from answer.com)