This is the 8597th most frequent Russian word.
оля
"Oля" is a diminutive form of the female name "Olga" in Russian.
'Оля' here is used as a proper noun, a typical Russian female name.
Оля пишет письмо своему другу.
Olya is writing a letter to her friend.
'оля' in this sentence appears to represent a poetic or regional term for a grove, albeit less common.
На горизонте виднелись оля и луга.
On the horizon, groves and meadows were visible.
Here, 'олю' is used in the accusative case of a feminine noun, likely meaning a grove or a small wood, fitting the setting description.