Dan....there are 2 usual uses for the word "zen".
1.Robert M. Pirsig's book entitled "Zen and the Art of Motorcycle Maintenance" helped bring the word to prominence in the West. Today, after many morphs, it is typically used to mean "thinking without thinking" or putting your brain on "cruise control".
2. Zen is a practice sect in the Buddhist philosophy/religion. Very esoteric and inexplicable. Example: Before one practices Zen, mountains are mountains and rivers are rivers. With some schooling mountains are no longer mountains and rivers are no longer rivers. Once you have journeyed in Zen, moutains are again moutains and rivers are again rivers.
Thats the best I can do!