Spiritual master is addressed as Om Vishnupada or Prabhupada

Satsvarupa Dasa: The name Prabhupada doesn't refer only to His Divine Grace A.C. Bhaktivedanta Swami Prabhupada. Previous Vaishnava acaryas such as Bhaktisiddhanta Sarasvati Thakura, Rupa Gosvami, and many others are also known as Prabhupada. In this verse, the word Prabhupada, referring to Sri Caitanya Mahaprabhu, is significant. Regarding this, Srila Bhaktisiddhanta Sarasvati Gosvami Prabhupada comments, "Sri Caitanya Mahaprabhu is the Supreme Personality of Godhead Himself, Sri Krishna, and all His servants address Him as Prabhupada. This means that there are many prabhus taking shelter under His lotus feet." The pure Vaishnava is addressed as prabhu, and this address is an etiquette observed between Vaishnavas. When many prabhus remain under the shelter of the lotus feet of another prabhu, the address Prabhupada is given. Sri Nityananda Prabhu and Sri Advaita Prabhu are also addressed as Prabhupada. Sri Caitanya Mahaprabhu, Sri Advaita Prabhu, and Sri Nityananda Prabhu are all vishnu-tattva, the Supreme Personality of Godhead, Lord Vishnu. Therefore all living entities are under Their lotus feet. Lord Vishnu is the eternal Lord of everyone, and the representative of Lord Vishnu is the Lord's confidential servant. Such a person acts as the spiritual master for neophyte Vaishnavas; therefore the spiritual master is as respectable as Sri Krishna Caitanya or Lord Vishnu Himself. For this reason, the spiritual master is addressed as Om Vishnupada or Prabhupada.