“Wahe Guru Ji Ka Khalsa, Wahe Guru Ji Ki Fateh” means “our purity belongs to God and our victory belongs to God.”
This is the Khalsa greeting. Sikhs also shout it out quite frequently at certain times during the worship services in the Gurdwara, and sometimes spontaneously call it out to express enthusiasm and approval.
It is a reminder to those who speak it and those who hear it, that we all belong to God, and God deserves the credit for any success (victory) we achieve. It affirms acknowledgment of God as the Doer.