Gurbani is the term used to describe a verse read from the Guru Granth Sahib, the holy book of Sikhism. Although verses belonging to other scriptures are also recited in a Sikh religious ceremony, they are not considered as Gurbani.
The Guru Granth Sahib is considered as the living guru of the Sikh religion. The verses from this Holy Scripture are believed to be the words of the guru. It is a written communication from the lord containing the path to true religion.
The reading of the Gurbani is part of the daily ritual in Sikh religion. During the recital, the people present in the congregation are supposed to pay attention to each word of the Gurbani and absorb the meaning in its completeness.