This is the 1576th most frequent Russian word.
серию
The word "серию" in English means "series" (accusative singular form).
Here, 'серию' refers to a single episode of a television series.
Я посмотрел новую серию любимого сериала.
I watched the new episode of my favorite series.
In this sentence, 'серию' is used to mean a collection or set of objects, in this case, posters.
Они решили создать серию красочных постеров для выставки.
They decided to create a series of colorful posters for the exhibition.
The word 'серию' here describes a sequence or set of books grouped together by topic or theme.