When Kasi Misra heard the proposal, he said, “I am very fortunate that Sri Caitanya Mahaprabhu, the Lord of all prabhus, will stay at my home.”

PURPORT: 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 Krsna, and all His servants address Him as Prabhupada. This means that there are many prabhus taking shelter under His lotus feet.” The pure Vaisnava is addressed as prabhu, and this address is an etiquette observed between Vaisnavas. 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 visnu-tattva, the Supreme Personality of Godhead, Lord Visnu. Therefore all living entities are under Their lotus feet. Lord Visnu is the eternal Lord of everyone, and the representative of Lord Visnu is the Lord’s confidential servant. Such a person acts as the spiritual master for neophyte Vaisnavas; therefore the spiritual master is as respectable as Sri Krsna Caitanya or Lord Visnu Himself. For this reason, the spiritual master is addressed as Om Visnupada or Prabhupada.

Srila Prabhupada’s rendering of Sri Caitanya-caritamrta Madhya-lila 10.23