This idea comes from the late Mahayana and refers to teachings contained in texts such as the White Lotus Sutra and the Avatamsaka Sutra which claim to unite all the different teachings into a single great way. Hence they are callled Ekayana which is Sanskrit for 'one vehicle'
Shravakayana: The Hearer vehicle; practitioners are liberated as Arahants - originally the term Arahant was virtually equivalent to Buddha, but over time it became degraded until it was seen as a distinctly inferior attainment.
Pratyekayana: The Solitary vehicle; practitioners are liberated as Pratyeka Buddhas, that is solitary buddhas who do not pass on their insights.
Bodhisattvayana: The Boddhisattva vehicle; practitioners are liberated as Buddhas.
A second better known classification came into use with the rise of the Vajrayana, which created a hierarchy of the teachings with the Vajrayana being the highest path. The Vajrayana itself become multilayered especially in Tibetan Buddhism.
In this list each yana is also talked about as a "turning of the wheel" which is a traditional India reference to the teaching of the Dharma. In the Pali Canon the first teaching is called the Dhammacakkappavatana Sutta or the First Turning of the Wheel of the Buddhist Teaching. The Mahayana then styled itself as a second, turning of the wheel, and the Vajrayana a third.
The Nyingma school of Tibetan Buddhism has nine yanas, a list made by combining the first type of three yanas, and adding the six classes of tantras.
Vajrayana (consisting of)
Upatantra (Tibetan spyod rgyud) ‘practice tantra’ and the Ubhayatantra (gnyis ka’i rgyud), ‘dual tantra’, because it practices the view of the next vehicle, Yogatantra, together with the action of the former.