From the Introduction to "The Recorded Sayings of Zen Master Joshu: The First Full English Translation" [Translated and Introduced by James Green]

~ "Zen" is a Japanese name for a particular teaching tradition within the overall framework of Buddhism which came to Japan through China from India where it originated in the life of Gautama Buddha around 500 BCE.
~ Gautama was not born as "Buddha", that is "the enlightened one", in the sense that this was not an inherited title. Being Buddha was something he earned through spiritual exploration. His diligent spiritual quest brought him to what is traditionally called "enlightenment", a direct experience of the core reality of being wherein the apparent paradox of subject/object duality is resolved, and the underlying life force, which is both something and nothing at once, is perceived.
~ In the aftermath of his enlightenment experience, Gautama felt it was his duty to help others to the same experience and to enunciate his insight into the nature of human existence. Thus, he began to teach those who showed interest. The foundation of his teaching was that having a similar enlightenment would create a release from suffering and spiritual anxiety — a nirvana, a state of being free from this suffering and spiritual anxiety. (p. xv)


— James Green, from the Introduction to "The Recorded Sayings of Zen Master Joshu" [9780761989851, Altamira Press, Walnut Creek, CA, 1998.]