More often that not, when I tell someone that I study Zen Buddhism, they nod at me like they know what I'm saying, but I can see that, in their eyes, they really don't know the difference.
Let me explain about Zen Buddhism and why I chose to study Zen, instead of other forms of Buddhism like Vajrayana (which is Tibetan Buddhism... basically a form of Mahayanic - Tantric Buddhism):
Before Buddhism came to Japan, it had become very popular in China. The Japanese sent those wanting, and willing, to learn Buddhism the schools in China and eventually developed the meditation-based practice of Zen. The samurai wanted to become focused, fearless, and enlightened so that they could master their craft and, so, studied Zen. Zen is a part of the Mahayana branch.
I study Zen because of it being such a meditation-based school of Buddhism. I find it extremely calming, relaxing, and I absolutely feel more focused when I immerse myself into Zen. I find that Zen also teaches me to let things go!
Many other attributes of the Japanese lifestyle fused into Zen matter much to me, like The Way of Tea.
Keep in mind, however, that this is my interpretation of Zen and how it works for me.