“Bole So Nihal” is translated as “The one who speaks shall be blessed.” It is traditionally called out by Sikhs on occasions when a unifying Sikh affirmation is desired. The answering call from the full congregation is “Sat Siri Akal” which means “Great undying Truth.”
~ Sikh Dharma International Glossary (https://www.sikhdharma.org/glossary/).