This is the 8918th most frequent Russian word.
псковскую
"Псковскую" refers to something related to Pskov, a city or region in Russia.
Here, 'Псковскую' is an adjective in the accusative case, describing the fortress of Pskov.
Я посетил Псковскую крепость во время своего путешествия.
I visited the Pskov fortress during my trip.
In this sentence, 'Псковской' is an adjective in the prepositional case, associated with the region.
Мы говорим о Псковской области, изучая географию.
We are talking about the Pskov region while studying geography.
The word 'Псковскую' here is an adjective in the accusative case, qualifying the church.