Short answers, pulled from the story.
Zen derives from the Japanese pronunciation of the Middle Chinese word chan, which in turn comes from the Sanskrit dhyana, meaning contemplation, absorption, or meditative state. The Chinese term for the Zen school is Chanzong, meaning meditation school. The lowercase zen was added to the Merriam-Webster dictionary in 2018 to describe a peaceful and calm worldview or attitude.
Chan is traditionally believed to have been brought to China by Bodhidharma, described in the sources as a semi-legendary Indian or Central Asian monk. From China, Chan spread south to Vietnam as Thien, northeast to Korea as Seon, and east to Japan as Zen.
Silent illumination, associated with Hongzhi Zhengjue (1091-1157) and the Caodong school, is an objectless meditation in which practitioners rest in open, non-dual awareness without fixing attention on any particular object. Koan practice, developed by Dahui (1089-1163) in the Linji school, involves concentrated contemplation on a single word or phrase from a recorded master-student dialogue. The two methods have historically been presented as rivals, though Dahui himself did not entirely condemn quiet sitting.
Dharma transmission is a formal procedure in which a Zen master authorizes a disciple as a direct successor, linking them to a lineage traced back to the Buddha. Critics from within the tradition, including masters Linji and Ikkyu, reportedly refused to receive transmission certificates. Modern Chinese Buddhist thinkers Taixu, Tanxu, and Yinshun argued that the practice promoted sectarianism and had no basis in the Buddha's original teaching.
According to Hori, the traditional Japanese Rinzai koan curriculum can take fifteen years to complete for a full-time monk. Students work through a standardized sequence of koans, presenting their understanding in private interviews with the teacher and memorizing sets of capping phrases matched to each koan.
Esoteric practices including mantras, dharanis, and ritual forms have been part of Zen since the Tang dynasty, with evidence from Dunhuang showing early Chan Buddhists adopted methods from Chinese Esoteric Buddhism. The Soto monk Keizan Jokin (1264-1325) was a major promoter who introduced numerous esoteric ritual forms into the Soto school under the influence of Shingon and Shugendo. The Shangama Mantra, preserved since the Tang period, continues to be chanted as part of morning and evening liturgy in modern temples.