Zen is many things. It is the history, philosophy and practice of Zen Buddhism, and also the source of all existence. It is sitting meditation. It is a generally peaceful state of mind. It is also a word that rhymes with ten, hen, then, when and again. It is nothing at all.
As the source of all existence, Zen encompasses everything, yet Zen philosophy teaches that the source of all existence is nothing. The aim of the practice and philosophy of Zen Buddhism is to help everybody in the world to directly experience Zen, the source of all existence, nothing, and thereby end their suffering.
The practice of Zen is sitting in meditation, walking in meditation, and living in meditation. Meditation is the practice of watching your mind. Your mind is like a giant vacuum that sucks you into whatever it thinks. Sitting meditation is like dropping an anchor, so that you don’t get completely sucked into whatever you happen to be doing with your mind. There is also walking meditation which can help you get up from your seated position while maintaining your anchor. Moving from sitting to walking meditation points the way to full life meditation, which is a constant recognition that everything that is happening is happening in your mind.
The philosophy of Zen follows the teaching of the Buddha who recognized that all this stuff happening in your mind causes suffering. He, and thousands of Buddhas after him, developed the philosophy of Zen and the practice of Zen to guide you to the experience of Zen, which helps you get beyond your mind and alleviate your suffering.
The way to get beyond your mind and alleviate suffering is to meditate, watch your mind, which means living in the present moment and observing all the strange and amazing places that your mind takes you. With enough practice, you will discover the peace of mind that is Zen, and you may directly experience the source of everything which is Zen. You will delight in the simple pleasures of your mind, which includes finding rhyming words like then, when, hen, and again, Zen. There’s nothing to it.