This is the 6182nd most frequent Turkish word.
ölü
Dead.
Here, the adjective 'ölü' describes the state of the bird being no longer alive, used attributively before a noun for descriptive purposes.
Bu sabah parkta ölü bir kuş buldum.
This morning, I found a dead bird in the park.
In this sentence, 'ölüler' is used as a noun referring to dead beings, pluralized to describe the subjects encountered.
O mağarada ölülerle karşılaştık, çok korkutucuydu.
We encountered the dead in that cave; it was very frightening.
Here, the word 'ölü' denotes an abstract noun form indicating the concept of being non-living or no longer alive, emphasizing the cyclical nature in existence.