This is the 15348th most frequent Korean word.
버스였는데
"It was a bus."
버스였는데 is used to indicate a past state (being a bus) with a contrastive nuance.
그것은 빨간색 버스였는데, 지금은 파란색으로 바뀌었어요.
It was a red bus, but now it has changed to blue.
버스였는데 indicates the bus' habitual presence in the past, introducing a change.
우리 학교 앞에 항상 있던 버스였는데, 이제 보이지 않아요.
It was the bus that was always in front of our school, but now it's not visible.
버스였는데 is used to highlight the change in choice of transportation.