In religious festivals of Gaudiya Vaishnavism Hari Bol is called out meaning: "Sing the name of Hari" or "Call out (or chant) the name of Hari". (Hari being the name for Krsna and Visnu)
From a more direct hindi translation: Bol = to speak, Hari = (a) god
It is used in many Hindi devotional songs.
Radha Ramana Hari Bol