This is the 5023rd most frequent Korean word.
기억을
"기억을" means "memory" (object form).
기억을 refers to 'memories' as the direct object of the verb 잃어버리다 (to lose).
그 당시의 기억을 잃어버렸습니다.
I lost the memories of that time.
기억을 acts as the direct object in the verb 구분하다 (to distinguish).
추억과 기억을 구분하는 것이 중요합니다.
It is important to distinguish between reminiscences and memories.
기억을 serves as the purpose of the action 간직하다 (to preserve).