This is the 3086th most frequent Russian word.
исторических
"Historical" or "of historical" (adjective form).
The word 'исторических' is here modifying 'документов' (documents), indicating these are documents of historical importance.
Студенты изучают значения исторических документов.
Students study the significance of historical documents.
Here, 'исторических' (historical) is used as an adjective to describe the artifacts related to history.
Мы посетили музей, полный исторических артефактов.
We visited a museum full of historical artifacts.
In this sentence, 'исторических' describes 'событиях' (events) that pertain to history.