In Tibetan Buddhism, “lineage” is a crucial component of the way in which the Dharma is transmitted and authenticated. It represents the heart-to-heart connection that has been passed down in an unbroken line from teacher to student.
There are said to be five different modes of this transmission of lineage and authority. The first of these is called the “thought lineage of the Conquerors,” the transmission directly from mind to mind without physical intermediary, a revelatory inspiration of a doctrine or a practice. The second is the “sign lineage of the ‘holders of the mantra,’” the transmission without speech by the use of manual signs and gestures. The third is the “ear-whispered lineage of humankind,” the oral transmission from ear to ear, a lineage of revelation passed on by a Master only to his chief disciples; it is this transmission of authority which forms the lineage of gurus of any particular sect, who communicate from generation to generation of Masters—as from Marpa to Milarepa to Gampopa—their special doctrines and contemplative revelations. A fourth is the “entrusted lineage of the dakinis”, the transmission especially of a hidden text composed by the Precious Guru Padmasambhava and entrusted to the guardianship of a dakini, who might hold the text for, say, five hundred years before passing it on to a “revealer of hidden texts,” and thus the gap between the original promulgation and its discovery does not “break the bridge” of its lineage. … [T]he fifth mode [is] called the “lineage of initiation, textual transmission, and instruction.” … [Having received initiation] one must hear [the text] in its entirety, read out loud by a teacher who had himself similarly heard it from his teacher. Thus the transmission of the text stretches in an unbroken line back to its author or to the Buddha himself, who first recited it to his disciples. It is not enough just to get the printed text, even when it is given by one’s Master; to be part of its lineage, and thus to be permitted its study and practice, it must actually be heard.
From Stephan Beyer The Cult of Tara, 399.
Each Tantric deity has its own unbroken lineage of practitioners. To be authentic and reliable this lineage must have had its source in the fully enlightened experience of a true master. Furthermore, this experience must have been passed down to us through an unbroken succession of adepts, each of whom attained realizations by accomplishing the practices of this deity. The strength of tantra—which has the literal meaning of ‘continuous’ or ‘continuity’—lies in its preservation and transmission of the enlightened experience through a continuous unbroken lineage of practitioners.
From Lama Yeshe Introduction to Tantra, 97.