Soen Sa Nim

Zen master is a somewhat vague English term that arose in the first half of the 20th century, sometimes used to refer to an individual who teaches Zen Buddhist meditation and practices, usually implying longtime study and subsequent authorization to teach and transmit the tradition themselves.

Until the Tang Dynasty, the term "Chánshī" (禅师; Dhyana Master) was regularly used for a monk who was a master of chan, or meditation, versus those who specialized in Dharma (scriptural teachings) and Vinaya (discipline and moral precepts). This included several important figures who were later not considered to be part of the "Chán school" per se, such as Tiantai Master Zhiyi.

In contemporary China, the term "Chán" (禪), being simply one of many terms for forms of meditation, is not limited to the Chán school alone. Neither the majority of monastics nor lay people are formally tied to a given "school" of Buddhist practice, which is different from the situation in Japan. It is only those senior and experienced practitioners who receive such transmission into the Chán school. Most temples belong to the Chán school in name, but also embrace other teachings including those of Tiantai, Pure Land, Huayan, and Yogacara schools, often under the umbrella term "Chinese Buddhism" (中國佛教). This has been the norm for the past 1000 years, since the Song Dynasty.

While there are no official organizations to regulate the use of honorary titles, "chánshī" is used as a title of respect for an adept, typically a monk, who specializes in Chán. "Chánzōng Dàshī" (禅宗大師; Great Master of the Chán School) is a similar and more specific honorary term, though rather rare. The same is true for the simple title "Dàshī" (大師; Great Master) which is rarely used to address a Dharma teacher (and any master of a specific craft or trade); the term is often bestowed posthumously by followers and students, although there are some exceptions (e.g. Hsing Yun).

...
Wikipedia