Zen. What is it? Officially, Zen is a school of Mahayana Buddhism. But it's so much more, at least in common culture. Taken from the above listed link to Wikipedia, "..Zen emphasizes rigorous meditation-practice, insight into Buddha-nature, and the personal expression of this insight in daily life, especially for the benefit of others. As such, it deemphasizes mere knowledge of sutras and doctrine and favors direct understanding through zazen and interaction with an accomplished teacher.." I don't know what zazen is, although it is an interesting "Z" word, nor do I feel like interacting with an accomplished teacher.
For me, Zen is a word that has come to describe the inner calm that is summoned when chaos is high and on the verge of overrunning your position. It's keeping your head in the game and being mindful of the present, when it would be all too easy to check out and give up.
In Zen, as in life, there is much to be made of staying calm and mindful.