Definition - What does Guru mean?
Guru is a term that is understood to mean "instructor" or "teacher." In the culture of yoga, however, the term has a much more profound meaning. The disciple of yoga considers a guru to be a trusted spiritual master. In many yoga traditions, an intimate relationship with one’s guru is akin to a relationship with the Divine and is considered to be fundamental to the achievement of enlightenment.
Yogapedia explains Guru
The word, guru, is a Sanskrit adjective that literally means, "heavy" or "venerable." The Hindu tradition uses the term to signify an intimate spiritual teacher who is "heavy" with knowledge and worthy of devotion; and, in the culture of yoga, a guru is regarded as an enlightened mentor.
In classic Indian traditions, the one-on-one relationship between the yoga disciple and the guru is considered paramount to the practice; and, in Western culture, gurus are revered as the link between Eastern holistic philosophy and the modern world.