This is the 11713th most frequent Russian word.
завершающего
"Finalizing" or "concluding."
The word 'завершающего' functions as an adjective to describe the act of the play that is the final one.
Кульминация наступила в завершающего акта пьесы.
The climax occurred in the concluding act of the play.
Here, 'завершающего' qualifies the statement as one that concludes a prior discourse.
Ученик изложил суть задачи в своём завершающего заявлении.
The student presented the essence of the task in his concluding statement.
In this example, 'завершающего' describes the stage of the research process that brings it to completion.