This is the 1035th most frequent Polish word.
szczecina
Bristle.
Here 'szczecina' refers to the coarse hairs found on certain animals, in this case, that of a wild boar.
Szczecina dzika jest ciemna i szorstka.
The bristle of the wild boar is dark and rough.
In this sentence, 'szczecina' is used to denote the bristles of a brush used for cleaning.
Szczecina ze szczotki świetnie czyści dywan.
The bristle from the brush cleans the carpet excellently.
Here, 'szczecina' refers to bristles that are specifically purchased for manufacturing artistic tools like paintbrushes.