In Satya, Treta, and Dvapara yugas, the Lord appears as the Supreme Lord. But in Kali-yuga, the Lord is hidden, He is channa-avatara. He is a hidden avatara. He doesn't assert Himself as the Supreme Personality of Godhead.
Why Lord Caitanya Tries to Remain Hidden - Gaura Purnima, February 28, 2010, Budapest