This is the 12879th most frequent Russian word.
левобережную
"Levoberezhnuyu" refers to "left-bank" or "located on the left bank" in English.
Here the word 'левобережную' functions as an adjective describing the 'part of the city' to indicate it is located on the left bank of a river.
Мы поехали в левобережную часть города.
We went to the left-bank part of the city.
In this sentence, 'левобережную' is used as an adjective modifying the noun 'территорию' (territory), specifying its geographical side along a river bank.
Левобережную территорию решили обустроить парками.
The left-bank territory was decided to be arranged with parks.
The word 'левобережную' here acts as an attributive adjective to the noun 'область', describing the aspect of location in relation to a river bank.