"For ice, the latent heat of fusion is 334 kJkg-1. This means that 334 kJ of heat is required to convert 1 kg of ice at 0ºC into 1 kg of water at 0ºC. Conversely, 334 kJ of heat is released when 1 kg of water freezes at 0ºC to give 1 kg of ice at 0ºC." So in this case 0oC is the atmospheric temp.?
This is the atmospheric temperature at which water freezes to ice and 334 kJ of heat is released to the surroundings.