Ajahn, Thai for teacher, is applied broadly to senior Buddhist monks in Thailand but carries particular significance within the Thai Forest Tradition, a reform and revival movement within Thai Theravada Buddhism emphasizing strict adherence to the Vinaya, intensive meditation practice, and, in its original form, a wandering, forest-dwelling monastic life deliberately distinct from the more settled, textually and ceremonially oriented monastic life common in many town and city temples. Ajahn Mun Bhuridatta, active in the early to mid twentieth century, is generally credited as the tradition's founding figure, whose intensive meditation practice and small circle of dedicated forest-dwelling disciples established the practice lineage and teaching style the tradition's later, far more widely known teachers carried forward.
An ajahn within this tradition typically heads a forest monastery, guiding resident monks' meditation practice through personal instruction reflecting his own direct experience rather than primarily through formal textual study, though Forest Tradition monasteries by no means reject scriptural study altogether; the emphasis on direct, teacher-guided meditation experience over purely academic training is a defining and frequently cited characteristic distinguishing the tradition's approach from some other strands of Thai monastic education.