This is the 9917th most frequent Russian word.
активного
"Активного" means "active" in English.
In this sentence, 'активного' modifies 'образ жизни,' describing the dynamic and energetic nature of his lifestyle.
Он ведет активного образ жизни.
He leads an active lifestyle.
Here, 'активного' qualifies 'участника,' indicating a person who is actively involved and engaged.
Я встретил активного участника в волонтерской программе.
I met an active participant in the volunteer program.
The word 'активного' describes 'ученика,' signifying the student's proactive and involved attitude.