This is the 45th most frequent Serbian word.
овог
The Serbian word "овог" means "of this" or "this" (genitive masculine or neuter singular form).
In this sentence, 'овог' is the genitive singular masculine form of the demonstrative pronoun, modifying 'дана' (the genitive singular masculine noun for 'day'). It indicates a specific day being referred to.
Овог дана су прошетали парком.
On this day, they took a walk in the park.
Here, 'овог' is again the genitive singular masculine form of the demonstrative pronoun, modifying 'месеца' (the genitive singular masculine noun for 'month'). It points to a specific month.
Овог месеца ћемо посетити музеј.
This month, we will visit the museum.
In this example, 'овог' is used as a masculine singular genitive form to match the noun 'писаоцу' (writer) and indicates that the writer being spoken of is specifically identified.