This is the 17125th most frequent Korean word.
생일을
"생일을" means "birthday" (as the object of a sentence).
In the third example, '생일을' serves as part of the phrasing '생일을 기념하다,' which means 'to commemorate the birthday.' It highlights the occasion being honored.
그녀에게 특별한 선물을 생일을 기념하여 주었어요.
I gave her a special gift in commemoration of her birthday.
In this sentence, '생일을' is used as a direct object for the verb '축하하다', which means 'to celebrate.' It refers specifically to the birthday being the event celebrated.
저는 친구의 생일을 축하해 주었어요.
I celebrated my friend's birthday.
Here, '생일을' acts as the direct object of the verb '보내다', meaning 'to spend.' It indicates the occasion that was spent.