Zen is a school of Mahayana Buddhism. It is primarily distinguished from other Buddhist sects in that it deemphasises religious texts as means to reaching enlightenment and instead focuses on introspection.
Zen emphasizes direct communication over the study of scripture.
In the words of Alan Watts, a British philosopher & writer:
"Zen does not confuse spirituality with thinking about God while one is peeling potatoes.
Zen spirituality is just to peel the potatoes."
The goal of Zen practice is to discover one's Buddha-nature. Practicing with others is seen as an important part.
Along the lines of spirituality in peeling potatoes, many Zen techniques are quite unconventional in comparison to what Westerners commonly perceive as spiritual practices.
Here are a few examples:
The core of Zen practice is the sitting meditation called Zazen (Japanese).
Sesshin, which literally means 'gathering the mind', refers to intensive group meditation in a Zen monastery.
Another famous Zen tradition is Koan (short stories, dialogues or questions), usually practiced during Zazen, or throughout daily life.
Katsu is a loud belly shout, which is today not such a common practice, but it belongs to the Zen heritage through various anecdotes.
"Before enlightenment: chop wood, carry water.
After enlightenment: chop wood, carry water."
Zen proverb