This is the 1982nd most frequent Korean word.
몸을
"몸을" means "body" (with an object marker).
Here, '몸을' means 'your body' and is used as the object of the verb 'to keep.'
몸을 건강하게 유지하기 위해 운동을 해야 해요.
You should exercise to keep your body healthy.
In this sentence, '몸을' indicates 'his body' as the object of the verb 'to move.'
그는 춤을 출 때 몸을 자유롭게 움직입니다.
He moves his body freely when he dances.
Here, '몸' refers to the physical body and is the object of the verb 'to wash.'