Recitation of the name of Amitabha Buddha. The central practice of all schools of Pure Land Buddhism. The nembutsu can be said in either the simple form (either 'Amida butsu' or just Amida), which truly is only the name of the Buddha Amida, or in a very slightly longer version that includes some Sanskrit/Pali borrow words:
Namo Amida Butsu
Which simply means 'homage (or praise) to the Buddha Amitabha'.
Different branches of the Pure Land teaching regard the nembutsu in slightly different ways. In the earliest teachings, the nembutsu was related directly to the idea of Amitabha Buddha's promise that any being who uttered his name at the time of their death would be reborn in his Western Pure Land. With increasing time and interpretation, particularly regarding the belief that Buddhism was entering the era of decline that the Japanese called mappo, the nembutsu became more abstract. For some, by constant repitition of the nembutsu, one accrued merit and earned rebirth in the Pure Land. Others saw it as supplicatory; by reciting the name of Amida, one begged for admittance to the Pure Land. Shinran, founder of the Jodo Shin Shu, taught that Amida Buddha had already made the decision to save all beings; the nembutsu was simply a way for one to build confidence in the strength of Amida's vow, and to offer thanks for his act of compassion. However, Shinran denied outright the possibility that saying the nembutsu influenced one's destination in rebirth, which he attributed solely to karma.
The nembutsu was probably the earliest Buddhist religious practice present in the United States in any number. Early Asian immigrants from China and Japan to the U.S in the 19th Century were largely lay Pure Land followers, and the first Buddhist churches and temples were built to allow them to recite the nembutsu at funerals, and on special occasions such as the anniversary of the deaths of Shinran and Honen.
The accesibility of the nembutsu is one of its most prominent characteristics. While other branches of Buddhism rely on the effort and abilities of the individual practitioner to achieve salvation (compare Theravada, in particular), the nembutsu requires no particular skill, learning, or knowledge of lanuage or theory. It can be said at any time, under any circumstances, silently or aloud, in a group or alone. Little wonder then that it is the primary form of religious observence for Buddhists from across the East Asian region where the Pure Land school is well established, and among immigrants from these regions