Real Dictionary

Zen
uncountable noun: Zen or Zen Buddhism is a form of the Buddhist religion that concentrates on meditation rather than on studying religious writings.

Zen in American English
a variety of Buddhism, now practiced esp. in Japan, Vietnam, and Korea, seeking to attain an intuitive illumination of mind and spirit through meditation, esp. on paradoxes
designating or of Zen Buddhism
noun: a Mahayana movement, introduced into China in the 6th century a.d. and into Japan in the 12th century, that emphasizes enlightenment for the student by the most direct possible means, accepting formal studies and observances only when they form part of su

Zen in British English
noun: a Japanese school, of 12th-century Chinese origin, teaching that contemplation of one's essential nature to the exclusion of all else is the only way of achieving pure enlightenment