This day is also called as Vyaasa Purnima . Maharishi Vyaasa was born on this full moon day. He completed the codification of the four Vedas on this day. He completed the writing of the eighteen puranas on this day.
In the term “Guru” –“Gu” means Gunateeta, one who is beyond attributes (gunas), “Ru” means Rupavarjita , implies one who is beyond forms (rupas). “Guru” is the one who reveals the “Guri” (target) to the disciple. “Guri” here refers to the Atmic Principle.
There is another interpretation for the word Guru. ‘Gu’ signifies darkness and ‘Ru’ denotes that which dispels darkness or ignorance (Gukaaro Andhakaarasya , Rukarasthannirodhakaha).