An āchārya teaches and sustains a tradition
Definition
The word āchārya is the title of someone who knows or teaches the rules (the āchāra), who is a spiritual guide or teacher, and who instructs yogic, religious and spiritual mysteries.
Meaning
An āchārya is usually someone who has lived and studied within a tradition and who has mastered that tradition.
As recognition of their achievement they are given the title of āchārya, in the same way that the title doctor in front of a name signifies certain qualifications.
The āchārya then becomes a senior member of that community, teaching as an authority, and also supporting the development of that tradition as a living, and evolving tradition.
Within the yoga and tantra traditions āchāryas provide the necessary physical, mental and spiritual preparation for higher spiritual teachings.
Application
There is a difference between a Guru and an āchārya and it is important to know this distinction. Too many people today are setting themselves up as gurus without understanding the harm they are doing.
An authentic spiritual guru is someone who has achieved an exalted degree of self-realization and who can initiate the disciple. Initiation creates an internal link with the guru and empowers the disciple, giving a clear direction for their life. The guru then functions at a psychic and spiritual level within the life of the disciple rather than at a material or temporal level.
In the spiritual traditions an āchārya does not initiate or give spiritual experience, that is the role of the guru. The āchārya teaches, gives information and technical and spiritual guidance. He or she may teach a vidyā, such as yoga, Ayurveda or jyotish. The āchārya is a spiritual guide or teacher in the more practical aspects of spirituality rather than in the higher and transcendent aspects which are the governance of the guru.
The guru may or may not teach the disciple, depending on their need. That is, the guru can also be an āchārya.