There are many explanations of the meaning of “guru,” and here is one of them, given by Srila Prabhupada in the Srimad Bhagavatam in his purport to 8.24.48: “Sri Caitanya Mahaprabhu therefore gives a definition of guru. Yare dekha, tare haha ‘krsna’-upadesa: the bona fide guru is he who advises his disciples exactly in accordance with the principles spoken by Krsna. The bona fide guru is he who has accepted Krsna as guru. This is the guru-parampara system. The original guru is Vyasadeva because he is the speaker of Bhagavad-gita and Srimad-Bhagavatam, wherein everything spoken relates to Krsna…The mission of the guru is the mission of the Supreme Personality of Godhead: to spread Krsna consciousness all over the world.”