The book is called White Nights because of the bright nights of early summer in St. Petersburg, when the sun dips just below the horizon and the sky never fully darkens. These are the nights in which the Dreamer's four meetings with Nastenka take place, all in the open air, on the embankment of a canal.
The expression hardly appears in the text. It appears only once, on the Third Night, when the Dreamer, writing on a rainy day on which he will not see Nastenka, begins to recount the meeting of the day before: "Yesterday was our third meeting, our third white night...". He uses the possessive our and counts the nights as one counts a possession.
What the book shows is the regime of those nights. The novella opens on a marvellous night, starry and clear, of the kind that, the narrator says, exist only when one is young. The meetings take place at night and end in farewells before dawn, and the last part of the book is called The Morning and begins by saying that the nights are over, on a rainy morning.
The white night is a time that is neither day nor night, and it is the exact time of the Dreamer: reverie, a life that is neither wholly real nor wholly invented. Some read the title only as a setting, the St. Petersburg of early summer, and others read it as an image of a happiness too clear to last, which ends when ordinary light returns. The text sustains both readings.