Zen is arguably one of the more cherished words within the lexicon of popular culture, applied as it is to things as diverse as home décor and motorcycle maintenance. Despite the new-age vibe that Zen appears to give, it is in fact a religion that is more than 13 centuries old now.
The word Zen is the Japanese translation of the Chinese word “Chan,” which is the name of a school of Buddhism which originated in China. As its etymology suggests, Zen was imported to Japan from China around 660. While its inception was rocky, Zen became Japan’s leading religious institution by the early 14th century. Later on, figures such as D.T. Suzuki and Shaku Soen introduced Zen to the Western world, where it was promptly taken up, though not without distortion, by beat generation writers like Jack Kerouac, beatniks and hippies.
At the heart of Zen lays the belief that every person has the potential to become a buddha, and that this enlightenment is achieved by meditation, contemplation and intuition. The goal of meditation is for people to be able to see their true nature, or kensho. Although the different Zen schools vary in their approach to enlightenment, they think that the cultivation of the self should continue even after one has attained enlightenment, and even be integrated into daily life.
More generally speaking, Zen is a branch of Mahayana Buddhism. It thus shares some similarities with the latter, such as in sutras (or scripture) and fundamental beliefs like the Four Noble Truths and the Eightfold Path, among others.
Constant meditation is imperative for Zen believers. While zazen translates to sitting meditation, it is more than just that. The aim of zazen is to settle the wandering and confused mind, thus bringing it closer to kensho. One practice of zazen centers on breathing, where the person calms his mind by counting his breaths, all the while paying attention to his posture. Another is shikantanza, or just-sitting meditation, where one simply sits in quiet meditation without overtly focusing on breath or posture.
Another practice of zazen is the contemplation of koans. Koans are pedagogical riddles that aim to push the believer further toward kensho. Koans are often given by Zen masters (usually of the Rinzai school) as one way to guide their students in attaining enlightenment.
Sources: Encyclopedia of Buddhism, Encyclopedia of Religion, zenguide.com