Full moon day during Ashadha month is known as Guru Purnima day. Traditionally this day is reserved for Guru Puja or Guru Worship. On this day disciples offer Puja or pay respect to their Gurus. Guru refers to guide who enlighten disciples by his knowledge and teachings.
Guru Purnima is also known as Vyasa Purnima and this day is commemorated as birth anniversary of Veda Vyasa.