This is the 14098th most frequent Polish word.
poziome
Horizontal.
The word 'poziome' is used as an adjective modifying 'linie' to describe their orientation as horizontal.
Ten obraz ma poziome linie.
This painting has horizontal lines.
Here, 'poziome' (adjusted to 'poziomym') indicates the spatial layout of the shelves, specifically their flat, horizontal orientation.
Zainstalowałem nowe półki w układzie poziomym.
I installed new shelves in a horizontal arrangement.
In this sentence, 'poziome' is describing the contours as being parallel to the horizon or in a flat orientation.