This is the 1121st most frequent Swedish word.
östra
Eastern.
In this sentence, 'östra' is used as an adjective describing the directional attribute (eastern) of the city's part.
Den östra delen av staden är mycket naturskön.
The eastern part of the city is very picturesque.
Here, 'östra' again serves as an adjective describing 'området' (area) as being in the eastern direction.
Vi bor i det östra området, nära skogen.
We live in the eastern area, near the forest.
In this example, 'östra' is used as a proper adjective defining the geographical region ('Europa') specifically as the eastern part.