My take on Zen. Reading the words of Roshi Robert Aitken on the subject what is Zen, prompted me to consider what is Zen to me?

Philosophy.
Zen is a philosophy. It is a way of thinking, yet not thinking. It is a way of being in the world, without worrying about being me. Who I am doesn't matter in Zen. Because in Zen, I does not exist.

Spiritual practice.
Constant practice of Zen is my spiritual practice. As sitting is my spiritual practice, so is reading, studying, eating, walking, living life in all of it's variety. The highs and the lows are all part of my Zen. Zen helps me live, and grow. It helps me face each day, no matter how terrible the day before may have been. It isn't magic, and in all honesty, it doesn't work all the time. But the times when it doesn't work are not a failing in Zen, they are a failing in me. Practice improves my success rate.

Lifestyle.
I live, eat, breathe and sleep Zen, it is my lifestyle. It is not something that I pick up occasionally, or practice at a certain time of day, or day of the week, it is how I live. It helps me to be calm, focused, make decisions, cope with difficulty. It helps me to be. Zen 24/7.