Lāma is a Tibetan word literally meaning 'the highest' or 'superior.' It is a title given to particularly esteemed Dhamma teachers, whether they be monks or layman, and also to those believed to be famous teachers of the past reborn into the present.
Ordinary monks are never called lāma. Tibetans take not three but four refuges, the first being 'I take refuge in the lāma.' This is a major departure from classical Buddhism and is a practice unique to Vajrayana.
- http://www.BuddhismA2Z.com/ Buddhism A to Z. Ven. Dhammika, 2007.