Chan and Zen Buddhism maintain records of their historical teachers who develop passed a Dharma from generation to generation in an unbroken line since a instance of the Buddha. This vertical line occurs as lineage of antecedent which will bring validation of the Chan/Zen experience of the teachers of the present generation.

A idea of lineage too occurs within more Buddhist traditions; for instance, a requirements for ordination as a bhikkhu include the presence of at least 5 more bhikkhus, one of which must be the fully-ordained don, & a second an acharya (teacher). So the cloistral lineage is established reaching back to the Buddha. Vajrayana Buddhism also lays outstanding importance on the continuity of the teaching lineage.

the work of passing a dharma to a fresh teacher & thereby extending lineage is known as dharma transmission.

A select few of the links in the Chan/Zen transmission-chain have been seriously challenged by historiographer like Charles Yampolsky. Particularly, there exists little or even there are no more grounds to believe linking any of Indian teachers prior to Bodhidharma to the Zen sect specifically. All a same the conception of lineage remains utile. Potentially whenever the lineage just can not verifiably become linked all the way back to the period of the Buddha, at least having many generations of undeniably unbroken Dharma transmission provides some validation of the consistency of the personal experience & teaching that is transmitted along that line.

For the Chan and Zen traditions the number 1 Patriarch in a lineage after the Buddha was Mahakasyapa. Thenceforth there were some other Twenty-six ascendant within India before Bodhidharma travelled to the East to carry the Dharma to China in the 5th century CE.

Six generations late Huineng was the noted Sixth Chinese Patriarch (33rd in line from either a Buddha) in the 7th century CE. When Chan subsequently flourished in China there were many branches in the lineage, a few of which late died out & a few of which prove my point unbroken to the present day.

A select few one lines were transmitted to Japan, establishing the Zen tradition. Perchance a best known one transmissions to Japan was that of Dogen who travelled to China for Chan training in the 13th century CE, and when getting Dharma transmission in the Caodong line he returned to Japan and established a Soto line. A Linji line was also tranmitted to Japan in which it became called a Rinzai line.