This is the 11782nd most frequent Russian word.
заключенных
"Prisoners" or "inmates."
Here, 'заключенных' is the genitive plural form of 'заключенный' (prisoner), used to denote prisoners.
Заключенных перевели в другую тюрьму.
The prisoners were transferred to another prison.
In this sentence, 'заключенных' is used in the genitive plural form to indicate prisoners in the context of their rights.
Доклад о правах заключенных был опубликован вчера.
The report about prisoners' rights was published yesterday.
The word 'заключенных' here is the plural genitive form, referring to prisoners who are receiving legal aid.