'White night' refers to a Summer night in the northern latitudes where the sun doesn’t set enough to cause full darkness. AKA beliye nochi in Russian.

It is also an idiom for a sleepless night, from the French Idiom nuit blanche, meaning the same thing ('white night' literally, 'sleepless night' figuratively).

Nosfentor reports that there is also a Spanish idiom, pasar la noche en blanco ('to pass the night in white'), which also means not being able to sleep.