This is the 3360th most frequent Russian word.
позади
"Позади" means "behind" or "at the rear."
In this sentence, 'позади' is used to indicate the spatial position of the book relative to the table, meaning 'behind'.
Книга лежит позади стола.
The book lies behind the table.
Here, 'позади' is employed metaphorically to signify that the hard times have been left in the past and are no longer a concern.
Мы оставили трудности позади.
We left the hardships behind.
In this example, 'позади' describes the relative position of the hikers, denoting 'behind' in a spatial sense.