This is the 7207th most frequent Korean word.
준비했던
"준비했던" means "had prepared."
In this sentence, '준비했던' describes the presentation that the speaker had prepared, using past-tense descriptive form to refer to prior preparation.
나는 준비했던 발표를 성공적으로 마쳤어요.
I successfully finished the presentation I had prepared.
Here, '준비했던' is used to describe a dish that the subject, she, had previously prepared, emphasizing her preparation effort in the past.
그녀가 준비했던 요리가 아주 맛있었어요.
The dish she had prepared was very delicious.
In this example, '준비했던' modifies '행사' (event), indicating an event that the subject 'we' prepared in the past, relating it to the context of participation in the present.