Yidam (Tib. ཡི་དམ་, Wyl. yi dam; Skt. iṣṭadevatā) — one of the three roots, the tutelary or chosen meditation deity, which is the root of spiritual accomplishment. Yidams are often classified according to whether they appear in peaceful and wrathful form.
Sogyal Rinpoche writes:
In Tibetan Buddhism practitioners will have a yidam, that is, a practice of a particular buddha or deity with which they have a strong karmic connection, which for them is an embodiment of the truth, and which they invoke as the heart of their practice. Since in their practice they have recognized the yidam as the natural radiance of the enlightened mind, they are able to view the appearances with this recognition, and let them arise as the deityCreativeMinds WordPress Plugin CM Tooltip Glossary