This is the 2081st most frequent Swedish word.
björk
Birch (a type of tree).
Here, 'björk' is used as a noun referring to the type of tree, a birch.
Det finns en björk i trädgården.
There is a birch in the garden.
Again, 'björk' serves as a noun, denoting a specific instance of a birch tree, with additional context of its location.
Björken vid sjön är väldigt gammal.
The birch by the lake is very old.
In this sentence, 'björkar' is the plural form of the noun 'björk', referring to multiple birch trees.