This is the 1964th most frequent Russian word.
совместных
"Совместных" means "joint" or "combined" in English.
The word 'совместных' is used here as an adjective in the genitive plural form, modifying 'мероприятий', emphasizing that the activities were jointly arranged or shared.
Мы организовали совместных мероприятий для детей.
We organized joint activities for the children.
Here, 'совместных' describes 'усилий' (efforts) and conveys that the efforts are shared or collaborative in nature.
Их общий проект требует совместных усилий.
Their joint project requires combined efforts.
In this sentence, 'совместных' applies to 'решений' (decisions) to denote that the decisions are made collectively.