This is the 8146th most frequent Russian word.
лидера
The Russian word "лидера" means "leader" in English.
Here, "лидером" is the instrumental case of "лидер", referring to a person in a leading position or role.
Молодой специалист был признан лидером команды.
The young specialist was recognized as the leader of the team.
In this sentence, "лидера" is used in the accusative case, indicating the direct object of the action.
Лидера избрали на собрании вчера.
The leader was elected at the meeting yesterday.
"Лидера" here is in the accusative case again, showing the object of our action of supporting.