This is the 16974th most frequent Russian word.
состоявшемся
"Состоявшемся" means "having taken place" or "successful/accomplished" depending on context.
In this sentence, 'состоявшемся' is used as an adjective modifying the noun 'собрания,' describing the meeting that has already taken place.
После состоявшемся собрания все участники почувствовали облегчение.
After the concluded meeting, all participants felt relief.
Here, 'состоявшемся' functions as an adjective modifying 'разговоре,' referring to the conversation that has already occurred.
Он размышлял о состоявшемся разговоре с другом.
He was reflecting on the conversation with a friend that had taken place.
In this example, 'состоявшемся' modifies the noun 'исследования,' describing the study as something completed.