This is the 437th most frequent Russian word.
всю
"Всю" – "all" or "whole" (feminine singular accusative form).
In this sentence, "всю" is used as an adjective in the accusative case to modify "книгу" (book), indicating the entirety of the object.
Я прочитал всю книгу.
I read the entire book.
Here, "всю" again acts as an adjective in the accusative case, emphasizing the total extent of "комнату" (room) that was cleaned.
Она убрала всю комнату.
She cleaned the entire room.
In this context, "всю" modifies "ночь" (night) in the accusative case, referring to the entirety of the time period discussed.